Semiconductor device

ABSTRACT

A semiconductor device using a pass transistor is provided. The semiconductor device includes a first circuit, a second circuit, a plurality of input terminals, and an output terminal. The first circuit includes a plurality of first transistors functioning as pass transistors, and the second circuit includes a plurality of second transistors functioning as pass transistors. Note that the number of the first transistors is larger than the number of the second transistors, a gate of the first transistor is supplied with a first signal, and a gate of the second transistor is supplied with a second signal. The first circuit is supplied with grayscale signals through x input terminals, and the first circuit selects y grayscale signals of the grayscale signals with the first signal. The second circuit is supplied with y (y&lt;x) grayscale signals, the second circuit outputs z (z&lt;y) grayscale signals of the y grayscale signals to the output terminal with the second signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application PCT/IB2021/051047, filed on Feb. 10, 2021, which is incorporated by reference and claims the benefit of a foreign priority application filed in Japan on Feb. 21, 2020, as Application No. 2020-028606.

TECHNICAL FIELD

One embodiment of the present invention relates to a semiconductor device.

Note that one embodiment of the present invention is not limited to the above technical field. Examples of the technical field of one embodiment of the present invention disclosed in this specification and the like include a semiconductor device, a display device, a light-emitting device, a power storage device, a memory device, an electronic device, a lighting device, an input device, an input/output device, a driving method thereof, and a manufacturing method thereof. A semiconductor device generally means a device that can function by utilizing semiconductor characteristics.

BACKGROUND ART

In recent years, display devices have been required to have higher definition in order to display high-resolution images. In addition, display devices used in information terminal devices such as smartphones, tablet terminals, and laptop PCs (personal computers) have been required to have higher multifunctionality as well as higher definition. For example, display devices have been required to have a variety of functions such as a touch panel function and a function of capturing images of fingerprints for authentication, in addition to a function of displaying images.

For example, Patent Document 1 discloses a semiconductor device that outputs a grayscale signal with use of a pass transistor logic.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No. 2017-223947

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

An object of one embodiment of the present invention is to provide a semiconductor device having a function of selecting and outputting a grayscale signal. An object of one embodiment of the present invention is to provide a semiconductor device in which an increase in a circuit area is inhibited even when the output potential width of a grayscale signal is large. An object of one embodiment of the present invention is to provide a semiconductor device in which noise from a selection circuit that selects a grayscale signal is inhibited. An object of one embodiment of the present invention is to provide a semiconductor device that generates a ramp signal with a grayscale signal with a large output potential width.

An object of one embodiment of the present invention is to provide a digital-analog converter circuit using a semiconductor device in which noise from a selection circuit that selects a grayscale signal is inhibited. An object of one embodiment of the present invention is to provide an analog-digital converter circuit using a semiconductor device that generates a ramp signal with a grayscale signal having a large output potential width. An object of one embodiment of the present invention is to provide a source driver including the digital-analog converter circuit and the analog-digital converter circuit.

An object of one embodiment of the present invention is to reduce the number of components of an electronic device. An object of one embodiment of the present invention is to provide a display device, an imaging device, an electronic device, or the like that has a novel structure. An object of one embodiment of the present invention is to at least reduce at least one of problems of the conventional technique.

Note that the description of these objects does not preclude the existence of other objects. One embodiment of the present invention does not have to achieve all these objects. Objects other than these can be derived from the description of the specification, the drawings, the claims, and the like.

Means for Solving the Problems

One embodiment of the present invention is a semiconductor device including a first circuit, a second circuit, a plurality of input terminals, and an output terminal. The first circuit includes a plurality of first transistors functioning as pass transistors, and the second circuit includes a plurality of second transistors functioning as pass transistors. The number of the first transistors is larger than the number of the second transistors, and the first circuit is cascaded to the second circuit. A gate of the first transistor included in the first circuit is supplied with a first signal, and a gate of the second transistor included in the second circuit is supplied with a second signal. The first circuit is supplied with first grayscale signals having different potentials through x (x is a positive integer) input terminals, and the first circuit selects y (y is a positive integer and y<x) first grayscale signals of the first grayscale signals with the first signal. The second circuit is supplied with they first grayscale signals, and the second circuit outputs z (y is a positive integer and z<y) first grayscale signals of the y first grayscale signals to the output terminal with the second signal.

In the above, the first circuit includes a first n-channel transistor, a second n-channel transistor, a first p-channel transistor, and a second p-channel transistor. The second circuit includes a third n-channel transistor and a third p-channel transistor. The first signal is supplied to the first n-channel transistor and the first p-channel transistor, and an inverted signal of the first signal is supplied to the second n-channel transistor and the second p-channel transistor. It is preferable that the second signal be supplied to the third p-channel transistor, and an inverted signal of the second signal be supplied to the third n-channel transistor.

In the above, one of a source and a drain of each of the first n-channel transistor, the second n-channel transistor, the first p-channel transistor, and the second p-channel transistor that are included in the first circuit is supplied with the first grayscale signal through the input terminal. The other of a source and a drain of each of the third n-channel transistor and the third p-channel transistor that are included in the second circuit preferably outputs, to the output terminal, any one of the first grayscale signals supplied to the input terminal.

In the above, it is preferable that the other of the source and the drain of each of the third n-channel transistor and the third p-channel transistor that are included in the second circuit be electrically connected to a low-pass filter.

In the above, the low-pass filter includes a first resistor, a second resistor, and a capacitor. The other of the source and the drain of the third p-channel transistor is electrically connected to one electrode of the first resistor. The other of the source and the drain of the third n-channel transistor is electrically connected to one electrode of the second resistor. It is preferable that the other electrode of the first resistor and the other electrode of the second resistor be electrically connected to one electrode of the capacitor and the output terminal.

In the above, the semiconductor device further includes a third circuit. The third circuit includes a fourth n-channel transistor and a fourth p-channel transistor. One of a source and a drain of each of the fourth n-channel transistor and the fourth p-channel transistor is supplied with any one of the first grayscale signals as a second grayscale signal. The other of the source and the drain of the fourth p-channel transistor is electrically connected to the one electrode of the first resistor, and the other of the source and the drain of the fourth n-channel transistor is electrically connected to the one electrode of the second resistor. A gate of the fourth n-channel transistor is supplied with a third signal, and a gate of the fourth p-channel transistor is supplied with an inverted signal of the third signal. The one electrode of the first resistor and the one electrode of the second resistor is preferably supplied with the second grayscale signal as a precharge potential.

One embodiment of the present invention is a digital-analog converter circuit including a latch circuit, a plurality of boosting circuits, a selection circuit, and a buffer circuit. The selection circuit includes a pass transistor circuit, a voltage generation circuit outputting a plurality of potentials, and a low-pass filter. The pass transistor circuit includes a plurality of first transistors and a plurality of second transistors functioning as pass transistors. The number of the first transistors is larger than the number of the second transistors, and the first transistor is cascaded to the second transistor. A data signal supplied to the latch circuit is supplied to the boosting circuit, the boosting circuit generates a selection signal by boosting a potential of the data signal, and with the selection signal, the first transistor and the second transistor that are included in the pass transistor circuit are brought into an on state or an off state so that any one of the potentials generated by the voltage generation circuit is selected and output to the low-pass filter. It is preferable that the buffer circuit be supplied with the potential from which noise is removed by the low-pass filter and the buffer circuit output the potential.

Effect of the Invention

According to one embodiment of the present invention, a semiconductor device having a function of selecting and outputting a grayscale signal can be provided. According to one embodiment of the present invention, a semiconductor device in which an increase in a circuit area is inhibited even when the output potential width of a grayscale signal is large can be provided. According to one embodiment of the present invention, a semiconductor device in which noise from a selection circuit that selects a grayscale signal is inhibited can be provided. According to one embodiment of the present invention, a semiconductor device that generates a ramp signal with a grayscale signal with a large output potential width can be provided.

According to one embodiment of the present invention, a digital-analog converter circuit using a semiconductor device in which noise from a selection circuit that selects a grayscale signal is inhibited can be provided. According to one embodiment of the present invention, an analog-digital converter circuit using a semiconductor device that generates a ramp signal with a grayscale signal having a large output potential width can be provided. According to one embodiment of the present invention, a source driver including the digital-analog converter circuit and the analog-digital converter circuit can be provided.

According to one embodiment of the present invention, the number of components of an electronic device can be reduced. According to one embodiment of the present invention, a display device, an imaging device, an electronic device, or the like that has a novel structure can be provided. According to one embodiment of the present invention, at least one of problems of the conventional technique can be reduced.

Note that the description of these effects does not preclude the existence of other effects. One embodiment of the present invention does not have to have all these effects. Effects other than these can be derived from the description of the specification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a circuit diagram illustrating an example of a semiconductor device. FIG. 1B is a diagram illustrating an example of output with respect to input of the semiconductor device.

FIG. 2A is a circuit diagram illustrating an example of the semiconductor device. FIG. 2B is a circuit diagram illustrating an example of a semiconductor device.

FIG. 3 is a circuit diagram illustrating an example of the semiconductor device.

FIG. 4A is a block diagram illustrating an example of a digital-analog converter circuit. FIG. 4B is a block diagram illustrating an example of the digital-analog converter circuit.

FIG. 5 illustrates an example of a pixel circuit.

FIG. 6A, FIG. 6B, FIG. 6C, and FIG. 6D are diagrams illustrating an example of a method for operating the pixel circuit.

FIG. 7A is a diagram illustrating a structure example of a display device. FIG. 7B is a circuit diagram illustrating an example of a subpixel.

FIG. 8 is a diagram illustrating a structure example of a display device.

FIG. 9 is a circuit diagram illustrating an example of a pixel.

FIG. 10 is a circuit diagram illustrating an example of a pixel.

FIG. 11A is a circuit diagram illustrating an example of a method for arranging pixels. FIG. 11B is a diagram illustrating an example of a method for arranging light-emitting elements and light-emitting and light-receiving elements.

FIG. 12 is a circuit diagram showing an example of the pixel.

FIG. 13 is a diagram showing an example of a method for operating a display device.

FIG. 14 is a diagram showing an example of the method for operating a display device.

FIG. 15A to FIG. 15D are cross-sectional views illustrating examples of display devices. FIG. 15E to FIG. 15G are top views illustrating examples of a pixel.

FIG. 16A to FIG. 16D are top views illustrating examples of a pixel.

FIG. 17A to FIG. 17E are cross-sectional views illustrating examples of a light-emitting and light-receiving element.

FIG. 18A and FIG. 18B are cross-sectional views illustrating examples of a display device.

FIG. 19A and FIG. 19B are cross-sectional views illustrating examples of a display device.

FIG. 20A and FIG. 20B are cross-sectional views illustrating examples of a display device.

FIG. 21A and FIG. 21B are cross-sectional views illustrating examples of a display device.

FIG. 22A and FIG. 22B are cross-sectional views illustrating examples of display devices.

FIG. 23 is a perspective view illustrating an example of a display device.

FIG. 24 is a cross-sectional view illustrating an example of a display device.

FIG. 25 is a cross-sectional view illustrating an example of a display device.

FIG. 26A is a cross-sectional view illustrating an example of a display device. FIG. 26B is a cross-sectional view illustrating an example of a transistor.

FIG. 27A is a diagram illustrating a structure example of a display device. FIG. 27B and FIG. 27C are circuit diagrams of pixel circuits.

FIG. 28A and FIG. 28B are timing charts showing a method for driving a display device.

FIG. 29A, FIG. 29B, FIG. 29D, and FIG. 29F to FIG. 29H are diagrams illustrating structure examples of a display device. FIG. 29C and FIG. 29E are diagrams illustrating examples of images.

FIG. 30A and FIG. 30B are diagrams illustrating an example of an electronic device.

FIG. 31A to FIG. 31D are diagrams illustrating examples of electronic devices.

FIG. 32A to FIG. 32F are diagrams illustrating examples of electronic devices.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments will be described with reference to the drawings. Note that the embodiments can be implemented in many different modes, and it is readily understood by those skilled in the art that modes and details thereof can be changed in various ways without departing from the spirit and scope thereof. Thus, the present invention should not be construed as being limited to the following description of the embodiments.

Note that in structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and a description thereof is not repeated. Furthermore, the same hatch pattern is used for the portions having similar functions, and the portions are not especially denoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, the layer thickness, or the region of each component is exaggerated for clarity in some cases. Therefore, they are not limited to the illustrated scale.

Note that in this specification and the like, the ordinal numbers such as “first” and “second” are used in order to avoid confusion among components and do not limit the number.

A transistor is a kind of semiconductor elements and can achieve amplification of current or voltage, switching operation for controlling conduction or non-conduction, or the like. A transistor in this specification includes, in its category, an IGFET (Insulated Gate Field Effect Transistor) and a thin film transistor (TFT).

Functions of a “source” and a “drain” are sometimes replaced with each other when a transistor of opposite polarity is used or when the direction of current is changed in circuit operation, for example. Therefore, the terms “source” and “drain” can be switched in this specification.

Note that in this specification, an EL layer refers to a layer containing at least a light-emitting substance (also referred to as a light-emitting layer) or a stack including a light-emitting layer, provided between a pair of electrodes of a light-emitting element.

In this specification and the like, a display device that is one embodiment of a display device has a function of displaying (outputting) an image or the like on (to) a display surface. Therefore, the display device is one embodiment of an output device.

In this specification and the like, a substrate of a display device to which a connector such as an FPC (Flexible Printed Circuit) or a TCP (Tape Carrier Package) is attached, or a substrate on which an IC is mounted by a COG (Chip On Glass) method or the like is referred to as a display device module, a display module, or simply a display device or the like in some cases.

Note that in this specification and the like, a touch panel that is one embodiment of a display device has a function of displaying an image or the like on a display surface and a function of a touch sensor that senses the contact, press, approach, or the like of a sensing target such as a finger or a stylus with or to the display surface. Thus, the touch panel is one embodiment of an input/output device.

A touch panel can be referred to as, for example, a display device (or a display panel) with a touch sensor, or a display device (or a display panel) having a touch sensor function. A touch panel can include a display device and a touch sensor panel. Alternatively, a touch panel can have a function of a touch sensor in the display device or on the surface of the display panel.

In this specification and the like, a structure in which a connector and an IC are mounted on a substrate of a touch panel is referred to as a touch panel module or a display module, or simply as a touch panel or the like in some cases.

Embodiment 1

In this embodiment, a structure example of a semiconductor device of one embodiment of the present invention and a driving method thereof are described. First, as one embodiment of the present invention, a semiconductor device including a first circuit, a second circuit, an input terminal, and an output terminal is described.

The input terminal includes a first input terminal to a sixth input terminal, for example. The first input terminal to the fourth input terminal are each supplied with a potential with different magnitude. A first signal is supplied to the fifth input terminal, and a second signal is supplied to the sixth input terminal. Note that the potentials with different magnitude supplied to the first input terminal to the fourth input terminal are rephrased as grayscale signals in the description. Accordingly, the grayscale signal can be rephrased as a potential generated using a resistor string or capacitance division or a grayscale potential.

The first circuit includes a first n-channel transistor, a second n-channel transistor, a first p-channel transistor, and a second p-channel transistor that function as pass transistors. The second circuit includes a third n-channel transistor and a third p-channel transistor that function as pass transistors. Therefore, the number of the transistors included in the first circuit is larger than the number of the transistors included in the second circuit, and the transistors included in the first circuit are cascaded to the transistors included in the second circuit. For example, cascade connection means that the output of the first circuit is connected to the input of the second circuit. Therefore, the transistors included in the first circuit are cascaded to the transistors included in the second circuit; thus, it can be also said that the first circuit is cascaded to the second circuit.

Next, an electrical connection between the first circuit and the second circuit is described. One of a source and a drain of each of the first p-channel transistor, the second p-channel transistor, the first n-channel transistor, and the second n-channel transistor is electrically connected to the first input terminal to the fourth input terminal, respectively. The other of the source and the drain of the first p-channel transistor is electrically connected to the other of the source and the drain of the second p-channel transistor and one of a source and a drain of the third p-channel transistor. The other of the source and the drain of the first n-channel transistor is electrically connected to the other of the source and the drain of the second n-channel transistor and one of a source and a drain of the third n-channel transistor. The other of the source and the drain of the third p-channel transistor is electrically connected to the other of the source and the drain of the third n-channel transistor and the output terminal.

A first signal is supplied to a gate of each of the first p-channel transistor, the second p-channel transistor, the first n-channel transistor, and the second n-channel transistor that are included in the first circuit. A second signal is supplied to a gate of each of the third p-channel transistor and the third n-channel transistor that are included in the second circuit. More specifically, the first signal is supplied to the gate of each of the first p-channel transistor and the first n-channel transistor, and an inverted signal of the first signal is supplied to the gate of each of the second p-channel transistor and the second n-channel transistor. An inverted signal of the second signal is supplied to the gate of each of the third p-channel transistor and the third n-channel transistor.

The first circuit is supplied with a grayscale signal V1 to a grayscale signal V4 having different potentials through the first input terminal to the fourth input terminal. The first circuit selects two grayscale signals from the grayscale signal V1 to the grayscale signal V4 with the first signal. The second circuit is supplied with the two grayscale signals selected with the first signal. In accordance with the second signal, the second circuit can select any one of the selected two grayscale signals and output the signal to the output terminal. Therefore, any one of the grayscale signals supplied to the first input terminal to the fourth input terminal is selected and output to the output terminal.

Therefore, the grayscale signal supplied to the first input terminal or the second input terminal is output to the output terminal through the p-channel transistors functioning as pass transistors that are cascaded. The grayscale signal supplied to the second input terminal or the fourth input terminal is output to the output terminal through the n-channel transistors functioning as pass transistors that are cascaded.

The other of the source and the drain of the third p-channel transistor and the other of the source and the drain of the third n-channel transistor may be electrically connected to the output terminal through a low-pass filter. When output through the low-pass filter, the grayscale signal from which noise is removed can be output as the output signal.

The low-pass filter includes a first resistor, a second resistor, and a capacitor. The other of the source and the drain of the third p-channel transistor is electrically connected to one electrode of the first resistor. The other of the source and the drain of the third n-channel transistor is electrically connected to one electrode of the second resistor. The other electrode of the first resistor and the other electrode of the second resistor are electrically connected to one electrode of the capacitor and the output terminal. Note that the low-pass filter can be provided by cascading a plurality of low-pass filters. In the case of providing a plurality of low-pass filters, the time constants of the low-pass filters may be the same or different.

For example, in the case where a potential selected with the first signal and the second signal that are generated from a digital signal are output as a grayscale signal, the semiconductor device functions as a digital-analog converter circuit.

As another example, the output terminal can output in order from the largest potential to the smallest potential with the first signal and the second signal. As another example, potentials can be output to the output terminal in order from the smallest potential to the largest potential with the first signal and the second signal. Downslope output signals changing from a larger potential to a smaller potential or upslope output signals changing from a smaller signal to a larger signal can be used as a ramp signal used for an analog-digital converter circuit.

The semiconductor device can further include a third circuit. The third circuit includes a fourth p-channel transistor and a fourth n-channel transistor. One of a source and a drain of each of the fourth p-channel transistor and the fourth n-channel transistor is supplied with any one of the grayscale signal V1 to the grayscale signal V4. The other of the source and the drain of the fourth p-channel transistor is electrically connected to the one electrode of the first resistor, and the other of the source and the drain of the fourth n-channel transistor is electrically connected to the one electrode of the second resistor. A third signal is supplied to a gate of the fourth n-channel transistor, and an inverted signal of the third signal is supplied to a gate of the fourth p-channel transistor. Thus, the one electrode of the first resistor and the one electrode of the second resistor are supplied with any one of the grayscale signal V1 to the grayscale signal V4 as a precharge potential.

With the above structure, even when a voltage amplitude from the minimum grayscale to the maximum grayscale (hereinafter, referred to as a grayscale width) supplied to the output terminal is large, the voltage between the source and the drain of each of the p-channel transistor and the n-channel transistor can be high; thus, an on state and an off state of the transistor can be reliably controlled. Note that in the case where the area occupied by the semiconductor device is made small, the size of a channel formation region of the transistor is preferably made small. However, in the case where the size of the channel formation region of the transistor is small, there is a problem of high on-state resistance of the transistor. In the structure in which the transistors are cascaded and function as pass transistors, noise due to the influence of delay and reflection because of the on-state resistance might occur in the output signal. Therefore, in the case of handling a large grayscale width, when a low-pass filter is provided before the output terminal, a grayscale signal with reduced influence of noise due to the on-state resistance of the transistor can be output from the output terminal.

A precharge potential that is a potential similar to the output grayscale signal is preferably supplied to the one electrode of each of the first resistor and the second resistor that are included in the low-pass filter. Note that the precharge potential can be selected using any one or both of the first signal and the second signal.

Note that the other of the source and the drain of the fourth p-channel transistor is preferably connected to a wiring connecting the other of the source and the drain of the third p-channel transistor to the one electrode of the first resistor at a position closer to the first resistor than the center position of the wiring. The other of the source and the drain of the fourth n-channel transistor is preferably connected to a wiring connecting the other of the source and the drain of the third n-channel transistor to the one electrode of the second resistor at a position closer to the second resistor than the center position of the wiring. The influence of noise can be inhibited when the precharge potential is supplied to the position close to the first resistor and the second resistor.

Note that the semiconductor device in which the first circuit and the second circuit are cascaded to each other is described above; however, the number of the cascaded circuits is not limited thereto. The number of circuits to be cascaded is preferably determined in accordance with the required grayscale levels.

Next, a structure example of the semiconductor device of one embodiment of the present invention is described with reference to drawings.

FIG. 1A is a circuit diagram illustrating a semiconductor device 120. For example, the semiconductor device 120 includes a pass transistor circuit 121, a voltage generation circuit 122, and a low-pass filter 123. The pass transistor circuit 121 includes an input terminal In1 to an input terminal In8, an input terminal A0 to an input terminal A2, an output terminal Ot1, an output terminal Ot2, a circuit 121 a, a circuit 121 b, and a circuit 121 c.

The circuit 121 a includes an inverter circuit L1 and a transistor S1 to a transistor S8. The transistor S1 to the transistor S4 are p-channel transistors, and the transistor S5 to the transistor S8 are n-channel transistors. The circuit 121 b includes an inverter circuit L2 and a transistor S9 to a transistor S12. The transistor S9 and the transistor S10 are p-channel transistors, and the transistor S11 and the transistor S12 are n-channel transistors. The circuit 121 c includes an inverter circuit L3, a transistor S13, and a transistor S14. The transistor S13 is a p-channel transistor and the transistor S14 is an n-channel transistor. Note that the reference numerals of the circuit 121 a to the circuit 121 c are shown only in FIG. 1 and omitted in the other drawings.

For example, the input terminal A0 is electrically connected to a gate of each of the transistor S1, the transistor S3, the transistor S6, and the transistor S8. In addition, the input terminal A0 is electrically connected to a gate of each of the transistor S2, the transistor S4, the transistor S5, and the transistor S7 through the inverter circuit L1. The input terminal A1 is electrically connected to a gate of each of the transistor S9 and the transistor S12. In addition, the input terminal A1 is electrically connected to a gate of each of the transistor S10 and the transistor S1 through the inverter circuit L2. The input terminal A2 is electrically connected to a gate of each of the transistor S13 and the transistor S14 through the inverter circuit L3.

The input terminal In1 is electrically connected to one of a source and a drain of the transistor S1, the input terminal In2 is electrically connected to one of a source and a drain of the transistor S2, the input terminal In3 is electrically connected to one of a source and a drain of the transistor S3, the input terminal In4 is electrically connected to one of a source and a drain of the transistor S4, the input terminal In5 is electrically connected to one of a source and a drain of the transistor S5, the input terminal In6 is electrically connected to one of a source and a drain of the transistor S6, the input terminal In7 is electrically connected to one of a source and a drain of the transistor S7, and the input terminal In8 is electrically connected to one of a source and a drain of the transistor S8.

The other of the source and the drain of the transistor S1 is electrically connected to the other of the source and the drain of the transistor S2 and one of a source and a drain of the transistor S9 through a node N1. The other of the source and the drain of the transistor S3 is electrically connected to the other of the source and the drain of the transistor S4 and one of a source and a drain of the transistor S10 through a node N2. The other of the source and the drain of the transistor S5 is electrically connected to the other of the source and the drain of the transistor S6 and one of a source and a drain of the transistor S11 through a node N3. The other of the source and the drain of the transistor S7 is electrically connected to the other of the source and the drain of the transistor S8 and one of a source and a drain of the transistor S12 through a node N4.

The other of the source and the drain of the transistor S9 is electrically connected to the other of the source and the drain of the transistor S10 and one of a source and a drain of the transistor S13 through a node N5. The other of the source and the drain of the transistor S11 is electrically connected to the other of the source and the drain of the transistor S12 and one of a source and a drain of the transistor S14 through a node N6.

The other of the source and the drain of the transistor S13 is electrically connected to the output terminal Ot1 through a node N7. The other of the source and the drain of the transistor S14 is electrically connected to the output terminal Ot2 through a node N8.

The voltage generation circuit 122 includes an output terminal 122 a to an output terminal 122 h. The output terminal 122 a to the output terminal 122 h are electrically connected to the input terminal In1 to the input terminal In8 of the pass transistor circuit 121, respectively.

The low-pass filter 123 includes an input terminal 123 a, an input terminal 123 b, and an output terminal 123 c. The output terminal Ot1 of the pass transistor circuit 121 is electrically connected to the input terminal 123 a and the output terminal Ot2 is electrically connected to the input terminal 123 b.

The voltage generation circuit 122 outputs the grayscale signal V1 to the grayscale signal V8 from the output terminal 122 a to the output terminal 122 h. The pass transistor circuit 121 determines a path selected by a selection signal AD0 to a selection signal AD2 that are supplied to the input terminal A0 to the input terminal A2. The low-pass filter 123 inhibits noise included in the grayscale signal supplied to the input terminal 123 a or the input terminal 123 b, and outputs an output signal Pout from the output terminal 123 c. Thus, the output signal Pout is any one of the grayscale signal V1 to the grayscale signal V8 that are supplied to the input terminal In1 to the input terminal In8. In other words, the semiconductor device 120 has a function of an analog selection circuit or a digital-analog converter circuit. Note that in this specification and the like, an analog selection circuit is simply referred to as a selection circuit in some cases.

Note that transistors with high withstand voltage are preferably used as the transistor S1 to the transistor S14 that are included in the pass transistor circuit 121. For example, a potential with a larger grayscale width than that output from the voltage generation circuit 122 can be supplied between the gate and the source and between the drain and the source of the transistor. For example, a voltage higher than or equal to 3.3 V can be supplied between the gate and the source and between the drain and the source of the transistor, preferably a voltage higher than or equal to 5 V can be supplied.

FIG. 1B is a diagram illustrating an example of the output signal Pout with respect to the selection signal AD0 to the selection signal AD2 that are supplied to the pass transistor circuit 121. For example, in the case where “L” as the selection signal AD0, “L” as the selection signal AD1, and “H” as the selection signal AD2 are supplied to the input terminal A0 to the input terminal A2, the selection signal can be expressed as a selection signal AD [0, 0, 1]. Note that an n-channel transistor is turned on when “H” as the selection signal AD is supplied to a gate, and is turned off when “L” as the selection signal AD is supplied to a gate. Furthermore, a p-channel transistor is turned on when “L” as the selection signal AD is supplied to a gate, and is turned off when “H” as the selection signal AD is supplied to a gate.

In one embodiment of the present invention, when the selection signal AD [0, 0, 1] is supplied to the pass transistor circuit 121 illustrated in FIG. 1A, the grayscale signal V1 is output as the output signal Pout. When the selection signal AD [1, 0, 1] is supplied, the grayscale signal V2 is output as the output signal Pout. When the selection signal AD [0, 1, 1] is supplied, the grayscale signal V3 is output as the output signal Pout. When the selection signal AD [1, 1, 1] is supplied, the grayscale signal V4 is output as the output signal Pout. When the selection signal AD [0, 0, 0] is supplied, the grayscale signal V5 is output as the output signal Pout. When the selection signal AD [1, 0, 0] is supplied, the grayscale signal V6 is output as the output signal Pout. When the selection signal AD [0, 1, 0] is supplied, the grayscale signal V7 is output as the output signal Pout. When the selection signal AD [1, 1, 0] is supplied, the grayscale signal V8 is output as the output signal Pout. Note that a path to be selected can be changed by changing the connection between the n-channel transistor and the p-channel transistor that are supplied with the selection signal AD.

FIG. 2A is a diagram illustrating an example of the voltage generation circuit 122 and the low-pass filter 123.

For example, the voltage generation circuit 122 includes a resistor string, a terminal VH, and a terminal VL. In this embodiment, an example is described in which the resistor string includes a resistor R1 to a resistor R9. Note that the resistor string can be formed using the needed number of resistors in accordance with the kind of the grayscale signal output form the voltage generation circuit 122. Note that the resistor string can be formed by connecting a plurality of resistors in series or in parallel. Alternatively, the resistor string can be formed with a combination of series connection and parallel connection. Thus, the number of resistors included in the resistor string is not limited. In addition, the resistor string can be formed to have the same magnitude of the resistance value as a whole. Alternatively, the resistor string can be formed by combining a plurality of kinds of resistors with different magnitude of resistance values.

Note that the voltage generation circuit 122 can be formed by connecting a plurality of capacitors in series or in parallel. Alternatively, the voltage generation circuit 122 can be formed with a combination of series connection and parallel connection of a plurality of capacitors.

The terminal VH is electrically connected to one electrode of the resistor R1, the other electrode of the resistor R1 is electrically connected to one electrode of the resistor R2 and the output terminal 122 a, the other electrode of the resistor R2 is electrically connected to one electrode of the resistor R3 and the output terminal 122 b, the other electrode of the resistor R3 is electrically connected to one electrode of the resistor R4 and the output terminal 122 c, the other electrode of the resistor R4 is electrically connected to one electrode of the resistor R5 and the output terminal 122 d, the other electrode of the resistor R5 is electrically connected to one electrode of the resistor R6 and the output terminal 122 e, the other electrode of the resistor R6 is electrically connected to one electrode of the resistor R7 and the output terminal 122 f, the other electrode of the resistor R7 is electrically connected to one electrode of the resistor R8 and the output terminal 122 g, the other electrode of the resistor R8 is electrically connected to one electrode of the resistor R9 and the output terminal 122 h, the other electrode of the resistor R9 is electrically connected to the terminal VL. Note that the magnitude of the resistance values of the resistor R1 to the resistor R9 is preferably set in accordance with the magnitude of the grayscale signal output from the voltage generation circuit 122.

Note that a potential higher than or equal to the maximum potential of the grayscale width is preferably supplied to the terminal VH. In addition, a potential lower than or equal to the minimum potential of the grayscale width is preferably supplied to the terminal VL.

The low-pass filter 123 includes a resistor R10, a resistor R11, and a capacitor C1 in addition to the input terminal 123 a, the input terminal 123 b, and the output terminal 123 c.

The input terminal 123 a is electrically connected to one electrode of the resistor R10, the input terminal 123 b is electrically connected to one electrode of the resistor R11, and the other electrode of the resistor R10 is electrically connected to the other electrode of the resistor R11, one electrode of the capacitor C1, and the output terminal 123 c. The other electrode of the capacitor C1 is supplied with a fixed potential. For example, the other electrode of the capacitor C1 is preferably supplied with GND as the fixed potential.

The resistor R10 and the capacitor C1 function as an RC filter with respect to the grayscale signal supplied to the input terminal 123 a and can inhibit or reduce noise included in the grayscale signal supplied to the input terminal 123 a. In addition, the resistor R11 and the capacitor C1 function as an RC filter with respect to the grayscale signal supplied to the input terminal 123 b and can inhibit or reduce noise included in the grayscale signal supplied to the input terminal 123 b.

Note that the resistor R10 not only functions as a low-pass filter with respect to the grayscale signal supplied to the input terminal 123 a but also has a function of preventing reflection of the grayscale signal supplied to the input terminal 123 b. Furthermore, the resistor R10 has a function of preventing the grayscale signal supplied to the input terminal 123 a from colliding with the grayscale signal supplied to the input terminal 123 b. Thus, a proper magnitude of the resistance value of the resistor R10 is preferably selected in accordance with a time constant needed by the low-pass filter.

Note that the resistor R11 not only functions as a low-pass filter with respect to the grayscale signal supplied to the input terminal 123 b but also has a function of preventing reflection of the grayscale signal supplied to the input terminal 123 a. Furthermore, the resistor R11 has a function of preventing the grayscale signal supplied to the input terminal 123 b from colliding with the grayscale signal supplied to the input terminal 123 a. Thus, a proper magnitude of the resistance value of the resistor R11 is preferably selected in accordance with a time constant needed by the low-pass filter.

In one embodiment of the present invention, an RC filter that can be formed using a resistor and a capacitor is used as the low-pass filter, for example. Note that the low-pass filter is not limited to an RC filter. For example, the low-pass filter can be formed using a coil and a resistor. Alternatively, the low-pass filter can be formed using a resistor, a coil, and a capacitor. As another example, an amplifier to be described later can be provided with a function of a low-pass filter.

FIG. 2B is a circuit diagram illustrating a low-pass filter 123A that is different from the low-pass 123 illustrated in FIG. 2A. The low-pass filter 123A includes a low-pass filter LP1, a low-pass filter LP2, and a low-pass filter LP3. The low-pass filter LP1 includes the resistor R10, the resistor R11, and the capacitor C1. The low-pass point LP2 includes a resistor R12 and a capacitor C2. The low-pass filter LP3 includes a resistor R13 and a capacitor C3. Note that the low-pass filter LP1 corresponds to the low-pass filter 123 illustrated in FIG. 2A.

The low-pass filter LP2 and the low-pass filter LP3 can have the same time constant as the low-pass filter LP1. The low-pass filter LP2 and the low-pass filter LP3 can inhibit or reduce the frequency component of noise included in the grayscale signal supplied to the input terminal 123 a in stages, for example. Such a structure can inhibit or reduce the amplitude of noise compared with the case of using only the low-pass filter LP1.

Alternatively, the low-pass filter LP2 and the low-pass filter LP3 can have a time constant different from that of the low-pass filter LP1. The low-pass filter LP2 can have a time constant different from that of the low-pass filter LP3. For example, the low-pass filter LP2 can have a larger time constant than the low-pass filter LP1, and the low-pass filter LP3 can have a larger time constant than the low-pass filter LP1. The low-pass filter LP2 and the low-pass filter LP3 can inhibit or reduce different frequency components in noise included in the grayscale signal supplied to the input terminal 123 a in stages, for example. Such a structure can inhibit or reduce noise more than the case of using only the low-pass filter LP1.

Note that in the case where the time constant of the low-pass filter LP1 is the same as or smaller than the time constant of the low-pass filter LP2, the resistance values of the resistor R10 and the resistor R11 that are included in the low-pass filter LP1 can be larger than the resistance value of the resistor R12 included in the low-pass filter LP2, and the capacitance value of the capacitor C1 included in the low-pass filter LP1 can be smaller than the capacitance value of the capacitor C2 included in the low-pass filter LP2. When the resistance values of the resistor R10 and the resistor R11 are large, reflection of the grayscale signal can be inhibited.

FIG. 3 is a circuit diagram illustrating an example of a semiconductor device 120.

The semiconductor device 120 illustrated in FIG. 3 includes a pass transistor circuit 121A that is different from the pass transistor circuit 121 illustrated in FIG. 1A. The pass transistor circuit 121A differs from the pass transistor circuit 121 illustrated in FIG. 1A in including an input terminal Pre, an inverter transistor L4, a transistor S15, and a transistor S16. The transistor S15 is a p-channel transistor and the transistor S16 is an n-channel transistor.

For example, one of a source and a drain of the transistor S15 and one of a source and a drain of the transistor S16 are electrically connected to the input terminal In5. The other of the source and the drain of the transistor S15 is electrically connected to anode N7. The other of the source and the drain of the transistor S16 is electrically connected to a node N8. Note that the one of the source and the drain of the transistor S15 and the one of the source and the drain of the transistor S16 are electrically connected to the input terminal In5 in the example described in one embodiment of the present invention, but may be connected to another input terminal.

For example, the input terminal Pre is electrically connected to a gate of the transistor S16. In addition, the input terminal Pre is electrically connected to a gate of the transistor S15 through the inverter circuit L4.

For example, when “H” is supplied to the input terminal Pre, the transistor S15 and the transistor S16 are turned on. Consequently, the grayscale signal V5 supplied to the input terminal In5 is supplied to the node N7 and the node N8. Note that the grayscale signal supplied to the node N7 and the node N8 is not particularly limited. Different grayscale signals are preferably supplied to the node N7 and the node N8 as necessary. That is, the node N7 and the node N8 are precharged with the potential of the grayscale signal V5. Note that the potential used for precharging is hereinafter referred to as a precharge potential. In the case where the potential of the grayscale signal is changed greatly by the selection signal AD0 to the selection signal AD2 that are supplied to the pass transistor circuit 121A, noise is easily generated in the node N7 and the node N8. However, in the case where a change in the potential of the node is large and the node is precharged with the precharge potential, the change in the potential of the node is small. Thus, the potential of the node has an effect of preventing generation of noise because the potential of the node changes only by the difference between the precharge potential and a selected grayscale signal. The larger the grayscale width output from the voltage generation circuit 122 is, the greater the effect is.

FIG. 4A is a block diagram illustrating an example of a digital-analog converter circuit using the semiconductor device of one embodiment of the present invention. A digital-analog converter circuit 100 includes a level shifter circuit 110, a semiconductor device 120, a buffer circuit 130, and an output terminal OUT. Note that a digital signal DT is supplied from a latch circuit 140 to the digital-analog converter circuit 100. Note that the digital signal DT is supplied from a processor, a GPU (Graphics Processing Unit), or another LSI (Large-Scale Integration), for example.

The output from the latch circuit 140 is supplied to the level shifter circuit 110. Note that the digital signal DT supplied to the latch circuit 140 is quantized and thus has a plurality of bit widths. Therefore, the level shifter circuit 110 preferably includes the same number of level sifter circuits as the bit width. The level shifter circuit 110 can generate the selection signal AD whose amplitude width is converted from the amplitude width of a digital signal into one that can be handled by the semiconductor device 120. Thus, the semiconductor device 120 can output a grayscale signal selected with the selection signal AD. The buffer circuit 130 can increase the amount of current of the supplied grayscale signal. The grayscale signal with the increased amount of current is supplied to the output terminal OUT. Note that the buffer circuit 130 can have a function of the low-pass filter 123. The latch circuit 140 can be included in the digital-analog converter circuit 100.

FIG. 4B is a block diagram illustrating an example of the digital-analog converter circuit 100 in detail. The digital-analog converter circuit 100 further includes a wiring 120 a and a wiring 120 b. The level shifter circuit 110 includes a level shifter circuit 110_1 to a level shifter circuit 110_n in the case where the digital signal DT has n bits. Note that n is an integer of 2 or more. The semiconductor device 120 includes the pass transistor circuit 121, the voltage generation circuit 122, and the low-pass filter 123. The buffer circuit 130 includes an amplifier circuit 130 a and an output resistor 130 b. Note that the output resistor 130 b is not necessarily provided.

Next, electrical connection of the digital-analog converter circuit 100 is described in detail. The latch circuit 140 is electrically connected to the level sifter circuit 110_1 to the level shifter circuit 110_n. The level shifter circuit 110_1 to the level shifter circuit 110_n are electrically connected to the pass transistor circuit 121. The n-th power of two output terminals included in the voltage generation circuit 122 are electrically connected to the n-th power of two input terminals included in the pass transistor circuit 121. The pass transistor circuit 121 is electrically connected to a non-inverting input terminal of the amplifier circuit 130 a through the low-pass filter 123. The amplifier circuit 130 a is electrically connected to an inverting input terminal of the amplifier circuit 130 a and one electrode of the output resistor 130 b. The other electrode of the output resistor 130 b is electrically connected to the output terminal OUT of the digital-analog converter circuit 100.

The wiring 120 a is electrically connected to the level shifter circuit 110_1 to the level shifter circuit 110_n and the terminal VH of the voltage generation circuit 122. The wiring 120 b is electrically connected to the level shifter circuit 110_1 to the level shifter circuit 110_n and the terminal VL of the voltage generation circuit 122.

Next, an operation of the digital-analog converter circuit 100 is described in detail. In FIG. 4B, the case where the digital signal DT has n bits is described. The level shifter circuit 110 generates the selection signal AD with n level shifter circuits, the level shifter circuit 110_1 to the level shifter circuit 110_n, and can determine selection conditions of the pass transistor circuit 121.

The voltage generation circuit 122 outputs the n-th power of two grayscale signals V with different gray levels to the pass transistor circuit 121. The pass transistor circuit 121 selects one grayscale signal from the n-th power of two grayscale signals V with the selection signal AD. The grayscale signal is supplied to the non-inverting input terminal of the amplifier circuit 130 a through the low-pass filter 123.

The buffer circuit 130 can increase the amount of current of the supplied grayscale signal. The grayscale signal with the increased amount of current is supplied to the output terminal OUT through the output resistor 130 b.

Thus, with the use of the semiconductor device 120 of one embodiment of the present invention, a semiconductor device having a function of selecting and outputting a grayscale signal can be provided. Furthermore, with the use of the semiconductor device 120, a semiconductor device in which an increase in a circuit area is inhibited even when the grayscale range is large can be provided. In addition, with the use of the semiconductor device 120, a grayscale signal with a large output potential width can be easily handled. With the use of the semiconductor device 120, a semiconductor device that generates a ramp signal with a grayscale signal having a large output potential width can be provided. The semiconductor device 120 can provide a digital-analog converter circuit in which noise from a selection circuit that selects a grayscale signal is inhibited.

At least part of the structure examples, the drawings corresponding thereto, and the like exemplified in this embodiment can be implemented in combination with the other structure examples, the other drawings, and the like as appropriate.

Embodiment 2

This embodiment will describe structure examples and an example of a driving method of a display device of one embodiment of the present invention.

Structure Example 1

One embodiment of the present invention is a display device including a plurality of pixels arranged in a matrix. Each pixel includes one or more subpixels. Each subpixel includes one or more light-emitting and light-receiving elements.

A light-emitting and light-receiving element (also referred to as a light-emitting and light-receiving device) is an element having a function of a light-emitting element (also referred to as a light-emitting device) that emits light of a first color, and a function of a photoelectric conversion element (also referred to as a photoelectric conversion device) that receives light of a second color. The light-emitting and light-receiving element can also be referred to as a multifunctional element, a multifunctional diode, a light-emitting photodiode, a bidirectional photodiode, or the like.

A plurality of subpixels each including a light-emitting and light-receiving element are arranged in a matrix, whereby the display device can have a function of displaying images and a function of capturing images. Thus, the display device can also be referred to as a complex device or a multifunctional device.

FIG. 5 illustrates part of a pixel circuit that can be used for the subpixel including a light-emitting and light-receiving element. The pixel circuit includes a switch SW1, a switch SW2, a switch SW3, a transistor Tr1, a transistor Tr2, and a light-emitting and light-receiving element ME. Moreover, the pixel circuit preferably includes a capacitor CS1 and a capacitor CS2 as capacitors for holding electric charge.

The switch SW1, the switch SW2, and the switch SW3 are each an element that includes two terminals and can control conduction and non-conduction between the terminals.

One terminal of the switch SW1 is electrically connected to a gate of the transistor Tr1 and one electrode of the capacitor CS1. One of a source and a drain of the transistor Tr1 is electrically connected to a wiring AL, and the other is electrically connected to one terminal of the switch SW2. The other terminal of the switch SW2 is electrically connected to one electrode of the light-emitting and light-receiving element ME and one terminal of the switch SW3. The other terminal of the switch SW3 is electrically connected to a gate of the transistor Tr2 and one electrode of the capacitor CS2. The other electrode of the light-emitting and light-receiving element ME is electrically connected to a wiring CL.

A constant potential is preferably supplied to the other electrode of the capacitor CS1 and the other electrode of the capacitor CS2. As the constant potential, a potential VDD, a potential VSS, a ground potential, a reference potential, a common potential, or the like can be used.

In FIG. 5 , an anode of the light-emitting and light-receiving element ME is positioned on the switch SW2 side. In this case, a potential supplied to the wiring CL can be lower than a potential supplied to the wiring AL. Note that a cathode of the light-emitting and light-receiving element ME may be positioned on the switch SW2 side; in that case, the wiring CL can be supplied with a potential higher than a potential supplied to the wiring AL.

Although an example where n-channel transistors are used as the transistors is illustrated in FIG. 5 and the like, some or all of the transistors can be p-channel transistors. In that case, a variety of potentials or signals described below can be changed as appropriate in accordance with the change of the transistors.

The transistor Tr1 has a function of controlling a current flowing through the light-emitting and light-receiving element ME. The transistor Tr1 can control a current flowing through the light-emitting and light-receiving element ME in accordance with a potential supplied to its gate through the switch SW1. The light-emitting and light-receiving element ME can emit light with luminance corresponding to the current.

Electric charge (a potential) is transferred from the light-emitting and light-receiving element ME through the switch SW3 to a node to which the gate of the transistor Tr2 is connected. The conducting state of the transistor Tr2 is changed in accordance with the potential.

An example of a method for operating the circuit illustrated in FIG. 5 will be described below.

FIG. 6A illustrates an operation in a period during which a data potential is written to the gate of the transistor Tr1 (a data writing period). In the data writing period, the switch SW1 and the switch SW2 are turned on, and the switch SW3 is turned off Thus, the data potential is supplied to the gate of the transistor Tr1 through the switch SW1. In addition, the capacitor CS1 is charged at this time.

FIG. 6B illustrates an operation in a period during which the gate potential of the transistor Tr1 is held and the light-emitting and light-receiving element ME emits light in accordance with a current flowing through the transistor Tr1 (a holding and light-emitting period). In the holding and light-emitting period, the switch SW1 and the switch SW3 are turned off, and the switch SW2 is turned on. Thus, the current flowing through the transistor Tr1 flows into the light-emitting and light-receiving element ME through the switch SW2. In FIG. 6B, the path of current is indicated by a dashed arrow.

By turning off the switch SW3 in the data writing period and the holding and light-emitting period, the light-emitting and light-receiving element ME and the transistor Tr2 can be electrically insulated from each other.

FIG. 6C illustrates an operation in a period during which the light-emitting and light-receiving element ME receives light and electric charge is accumulated in the light-emitting and light-receiving element (a light exposure period). Electric charge is accumulated at both ends of the light-emitting and light-receiving element ME in the light exposure period, whereby a potential difference Vc between the anode and the cathode of the light-emitting and light-receiving element ME is changed.

In the light exposure period, the switch SW1, the switch SW2, and the switch SW3 are all turned off. Thus, the light-emitting and light-receiving element ME is electrically insulated from both the transistor Tr1 and the transistor Tr2. Consequently, the electric charge accumulated on the anode side of the light-emitting and light-receiving element ME can be prevented from flowing toward the transistor Tr1 and the transistor Tr2. As a result, image capturing with high accuracy can be performed.

Note that in the light exposure period, the switch SW1 may be turned on. In that case, data potential writing may be performed in the light exposure period. In other words, a period during which light exposure and data writing are concurrently performed may be provided.

FIG. 6D illustrates an operation in a period during which the electric charge accumulated in the light-emitting and light-receiving element ME is transferred to the node to which the gate of the transistor Tr2 is connected (a transfer period). In the transfer period, the switch SW1 and the switch SW2 are turned off, and the switch SW3 is turned on. Thus, the electric charge accumulated in the light-emitting and light-receiving element ME is transferred through the switch SW3 to the node to which the gate of the transistor Tr2 is connected. By turning off the switch SW3 after transfer of the electric charge is completed, the potential of the gate of the transistor Tr2 is held.

By turning off the switch SW2 in the transfer period, the light-emitting and light-receiving element ME and the transistor Tr1 can be electrically insulated from each other. Thus, as illustrated in FIG. 6D, a current can be prevented from flowing from the wiring AL through the transistor Tr1, the switch SW2, and the switch SW3 to the node to which the gate of the transistor Tr2 is connected. In particular, in the case where the data potential is held at the gate of the transistor Tr1 and the transistor Tr1 is on, turning off the switch SW2 can favorably prevent electric charge from flowing from the wiring AL to the gate of the transistor Tr2.

In the light exposure period and the transfer period, the data potential is preferably held at the gate of the transistor Tr1. Thus, by switching the switch SW2 from the non-conducting state to the conducting state after the transfer period ends, the light-emitting and light-receiving element ME can be made to emit light immediately without additional data writing. Accordingly, a period during which an image is not displayed (a non-display period) is not caused in the period after the transfer period is completed until an image is displayed; hence, degradation of display quality can be prevented.

In this manner, the switch SW2 is controlled to be turned on in a period during which an image is displayed, and to be turned off in a period during which image capturing is performed (the light exposure period and the transfer period). That is, the switch SW2 can be referred to as a switch for switching between image display and image capturing. By providing the switch SW2 between the transistor Tr1 and the light-emitting and light-receiving element ME, the functions of the light-emitting and light-receiving element ME can be reliably switched.

Structure Example 2

A more specific structure example of the display device of one embodiment of the present invention will be described below.

FIG. 7A illustrates a block diagram for describing a structure of a display device 10. The display device 10 includes a display portion 11, a driver circuit 12, a driver circuit 13, a driver circuit 14, a circuit 15, and the like. The digital-analog converter circuit described in Embodiment 1 can be used as the driver circuit 12.

The display portion 11 includes a plurality of pixels 30 arranged in a matrix. The pixel includes a subpixel 20R, a subpixel 20G, and a subpixel 20B. The subpixel 20R includes a light-emitting and light-receiving element, and the subpixel 20G and the subpixel 20B each include a light-emitting element.

A wiring SL1, a wiring GL, a wiring RS, a wiring SE, a wiring WX, and the like are electrically connected to the subpixel 20R. A wiring SL2, the wiring GL, and the like are electrically connected to the subpixel 20G. A wiring SL3, the wiring GL, and the like are electrically connected to the subpixel 20B.

The wiring SL1, the wiring SL2, and the wiring SL3 are electrically connected to the driver circuit 12. The wiring GL is electrically connected to the driver circuit 13. The wiring RS and the wiring SE are electrically connected to the driver circuit 14. The wiring WX is electrically connected to the circuit 15. The driver circuit 12 functions as a source line driver circuit (also referred to as a source driver) and supplies a data signal (data potential) to the subpixels through the wiring SL1, the wiring SL2, and the wiring SL3. The driver circuit 13 functions as a gate line driver circuit (also referred to as a gate driver) and supplies a selection signal to the wiring GL.

The driver circuit 14 has a function of generating a signal to be supplied to the subpixel 20R and outputting the signal to the wiring SE, the wiring RS, and the like. The driver circuit 14 also has a function of generating and outputting a signal to be supplied to a wiring REN and a wiring TX that will be described later. Note that the driver circuit 13 or the driver circuit 12 may have a function of generating a signal to be supplied to one or both of the wiring REN and the wiring TX. The circuit 15 has a function of receiving a signal output from the subpixel 20R through the wiring WX and outputting the signal to the outside as imaging data. The circuit 15 functions as a reading circuit.

[Configuration Example of Pixel]

FIG. 7B illustrates an example of a circuit diagram of the subpixel 20R. The subpixel 20R includes a circuit 22R, a circuit 22, and a light-emitting and light-receiving element MER. The circuit 22R includes transistors M1 to M3, a transistor M10, and a capacitor C1. The circuit 22 includes transistors M11 to M14 and a capacitor C2.

The circuit 22R functions as a circuit for controlling light emission of the light-emitting and light-receiving element MER when the light-emitting and light-receiving element MER is used as a light-emitting element. The circuit 22R has a function of controlling a current flowing through the light-emitting and light-receiving element MER in accordance with the value of a data potential supplied from the wiring SL1.

The circuit 22 functions as a sensor circuit for controlling the operation of the light-emitting and light-receiving element MER when the light-emitting and light-receiving element MER is used as a light-receiving element. The circuit 22 has a function of supplying a reverse bias voltage to the light-emitting and light-receiving element MER, a function of controlling the light exposure period of the light-emitting and light-receiving element MER, a function of holding a potential based on electric charge transferred from the light-emitting and light-receiving element MER, a function of outputting a signal based on the potential to the wiring WX, and the like.

A gate of the transistor M1 is electrically connected to the wiring GL, one of a source and a drain of the transistor M1 is electrically connected to the wiring SL1, and the other thereof is electrically connected to agate of the transistor M2 and one electrode of the capacitor C1. One of a source and a drain of the transistor M2 is electrically connected to the wiring AL, and the other thereof is electrically connected to one of a source and a drain of the transistor M10, the other of a source and a drain of the transistor M3, and the other electrode of the capacitor C1. A gate of the transistor M3 is electrically connected to the wiring GL, and one of the source and the drain of the transistor M3 is electrically connected to a wiring V0L. A gate of the transistor M10 is electrically connected to the wiring REN, and the other of the source and the drain of the transistor M10 is electrically connected to one electrode of the light-emitting and light-receiving element MER. The other electrode of the light-emitting and light-receiving element MER is electrically connected to the wiring CL.

A data potential is supplied to the wiring SL1. A constant potential is supplied to the wiring V0L. An anode potential is supplied to the wiring AL. A cathode potential is supplied to the wiring CL. In the configuration illustrated in FIG. 7B, the anode potential is higher than the cathode potential. A signal for controlling the conduction and non-conduction of the transistor M10 is supplied to the wiring REN.

A gate of the transistor M11 is electrically connected to the wiring TX; one of a source and a drain of the transistor M11 is electrically connected to the one electrode of the light-emitting and light-receiving element MER; and the other thereof is electrically connected to a gate of the transistor M13, one of a source and a drain of the transistor M12, and one electrode of the capacitor C2. A gate of the transistor M12 is electrically connected to the wiring RS, and the other of the source and the drain of the transistor M12 is electrically connected to a wiring VRS. The other electrode of the capacitor C2 is electrically connected to a wiring VCP. One of a source and a drain of the transistor M13 is electrically connected to a wiring VPI, and the other thereof is electrically connected to one of a source and a drain of the transistor M14. Agate of the transistor M14 is electrically connected to the wiring SE, and the other of the source and the drain of the transistor M14 is electrically connected to the wiring WX.

A signal for controlling conduction and non-conduction of the transistor M11 is supplied to the wiring TX. A constant potential is supplied to the wiring VCP. A reset potential is supplied to the wiring VRS. A constant potential is supplied to the wiring VPI. In the configuration illustrated in FIG. 7B, a reset potential supplied to the wiring VRS is preferably lower than the cathode potential supplied to the wiring CL.

Here, the transistor M10 corresponds to the switch SW2 in Structure Example 1 above and FIG. 5 ; the transistor M2 corresponds to the transistor Tr1; the transistor M13 corresponds to the transistor Tr2; the transistor M1 corresponds to the switch SW1; and the transistor M11 corresponds to the switch SW3.

Here, transistors with an extremely low leakage current in a non-conducting state are preferably used as the transistor M1, the transistor M3, the transistor M10, the transistor M11, the transistor M12, and the transistor M14, which function as switches. In particular, transistors including an oxide semiconductor in a semiconductor layer where a channel is formed can be favorably used. It is preferable to use transistors using an oxide semiconductor also as the transistor M2 and the transistor M13, in which case all the transistors can be formed through the same manufacturing steps. Note that as the transistor M2 and the transistor M13, silicon (including amorphous silicon, polycrystalline silicon, and single crystal silicon) may be used in a semiconductor layer where a channel is formed. Without limitation to the above, some or all of the transistors can be transistors using silicon. Alternatively, some or all of the transistors may be transistors using an inorganic semiconductor other than silicon, a compound semiconductor, an organic semiconductor, or the like.

FIG. 8 is a block diagram for describing a structure of the display device 10 different from that in FIG. 7A. The display device 10 includes the display portion 11, a driver circuit 12A, the driver circuit 13, the driver circuit 14, and the like. The driver circuit 12A can include a plurality of circuits 12R, a plurality of circuits 12G, a plurality of circuits 12B, and a plurality of circuits 15A. Note that the circuit 15A corresponds to the circuit 15 illustrated in FIG. 7A.

As the circuit 12R, the digital-analog converter circuit described in Embodiment 1 can be used. The circuit 12R includes a latch circuit 71, a level shifter circuit 72, a semiconductor device 73, a buffer circuit 74, and the like. Note that the circuit 12G and the circuit 12B have the same structure as the circuit 12R.

The circuit 12R can convert image data Data supplied to the driver circuit 12A into an image signal by digital-analog conversion and supply the image signal to the subpixel 20R through the wiring SL1. Note that the image signal is a grayscale signal that can be expressed by the magnitude of a potential.

The circuit 12G can convert the image data Data supplied to the driver circuit 12A into an image signal by digital-analog conversion and supply the image signal to the subpixel 20G through the wiring SL2. The circuit 12B can convert the image data Data supplied to the driver circuit 12 into an image signal by digital-analog conversion and supply the image signal to the subpixel 20B through the wiring SL3.

The circuit 15A has a function of an analog-digital converter circuit. The circuit 15A includes a reading circuit 81, a ramp generation circuit 82, a comparison circuit 83, and a counter circuit 84.

The reading circuit 81 has a function of receiving a reading signal output from the subpixel 20R through the wiring WX. The reading signal is detected as voltage. The comparison circuit 83 can compare a reading signal received by the reading circuit 81 and a ramp signal output from the ramp signal generation circuit 82. Note that the ramp signal generation circuit 82 outputs a downslope output signal described in Embodiment 1 as the ramp signal. Note that the ramp signal may be an upslope output signal.

As an example, the case where the ramp signal is a downslope output signal is described. The comparison circuit 83 can compare the reading signal and the ramp signal. When the reading signal is smaller than the ramp signal, an output signal of the comparison circuit 83 is inverted. In other words, the reading signal is quantized by counting, in the counter circuit 84, the time until the output signal of the comparison circuit 83 is inverted. Thus, the circuit 15A has a function of outputting the count value to the outside as imaging data Sout.

Thus, the driver circuit 12A is a source line driver circuit (also referred to as a source driver) including a detection circuit that detects imaging data.

FIG. 9 illustrates an example of a circuit diagram of the pixel 30 including the subpixel 20R, the subpixel 20G, and the subpixel 20B.

The subpixel 20G includes a circuit 22G and a light-emitting element ELG. The subpixel 20B includes a circuit 22B and a light-emitting element ELB.

The circuit 22G and the circuit 22B have the same configuration as the circuit 22R included in the subpixel 20R except that the transistor M10 is not included. In the circuit 22G and the circuit 22B, the other of the source and the drain of the transistor M2 is electrically connected to one electrode of the light-emitting element ELG or the light-emitting element ELB.

For example, in the pixel 30, the light-emitting and light-receiving element MER is an element that emits red light and receives green or blue light, the light-emitting element ELG is an element that emits green light, and the light-emitting element ELB is an element that emits blue light. That is, the light-emitting and light-receiving element MER preferably functions as a photoelectric conversion element that receives light emitted from one or both of the light-emitting element ELG and the light-emitting element ELB. Thus, one or both of the light-emitting element ELG and the light-emitting element ELB can be used as a light source when an image of a fingerprint or the like is captured with the light-emitting and light-receiving element MER. For example, when light emitted from the light-emitting element ELG or the light-emitting element ELB is reflected by a subject such as a finger and the reflected light is sensed by the light-emitting and light-receiving element MER, a clear image of the subject can be captured.

Note that a structure may be employed in which a transistor including a back gate is used as each transistor. A pair of gates (a gate and a back gate) can be electrically connected to each transistor in each transistor.

Note that the structure is not limited to a structure in which the pair of gates are electrically connected to each other in each transistor. As another example, a transistor in which one of a pair of gates is connected to another wiring may be included. For example, when one of the pair of gates is connected to a wiring supplied with a constant potential, the stability of electrical characteristics can be improved. One of the pair of gates may be connected to a wiring supplied with a potential for controlling the threshold voltage of the transistor. As another example, a transistor in which one of a pair of gates is connected to one of a source and a drain may be used. In this case, one of the gates is preferably connected to the source. Both a transistor having a back gate and a transistor not having a back gate may be included.

Structure Example 3

A structure example of a display device including a pixel having a configuration partly different from the above will be described below.

The pixel described below as an example is a pixel in which a light-emitting and light-receiving element and light-emitting elements can be made to emit light by using two kinds of data potentials. For example, grayscale can be corrected with one of the data potentials. A potential higher than the maximum potential that a source driver for supplying the two data potentials is capable of supplying can be generated in the pixel described below. Thus, the power supply voltage of the source driver can be lowered, so that the power consumption of the source driver can be reduced.

Structure Example 3-1

FIG. 10 is a circuit diagram of a pixel 30 a. The pixel 30 a includes a subpixel 20 aR, a subpixel 20 aG, and a subpixel 20 aB. Instead of the wiring GL, a wiring GL1 and a wiring GL2 are connected to the pixel 30 a. Moreover, a wiring VL1, a wiring VL2, and a wiring VL3 are connected to the pixel 30 a. The wiring GL1 and the wiring GL2 are electrically connected to the driver circuit 13. The wiring VL1, the wiring VL2, and the wiring VL3 are electrically connected to the driver circuit 12 or the driver circuit 12A.

The subpixel 20 aR includes a circuit 22 aR, the circuit 22, and the light-emitting and light-receiving element MER. The above description can be referred to for the circuit 22, which has a configuration similar to that in the subpixel 20R.

The circuit 22 aR includes a transistor M4 and a capacitor C3 in addition to the above-described circuit 22R. Similarly, the circuit 22 aG and the circuit 22 aB each include the transistor M4 and the capacitor C3.

A gate of the transistor M4 is electrically connected to the wiring GL2, one of a source and a drain of the transistor M4 is electrically connected to the wiring VL1, and the other thereof is electrically connected to one of the source and the drain of the transistor M3 and the other electrode of the capacitor C3. One electrode of the capacitor C3 is electrically connected to the other of the source and the drain of the transistor M1, the gate of the transistor M2, and one electrode of the capacitor C1. The gates of the transistor M1 and the transistor M3 are electrically connected to the wiring GL1.

In the circuit 22 aG, one of the source and the drain of the transistor M4 is electrically connected to the wiring VL2. In the circuit 22 aB, one of the source and the drain of the transistor M4 is electrically connected to the wiring VL3.

Different selection signals are supplied to the wiring GL1 and the wiring GL2. A first data potential DR is supplied to the wiring SL1. A second data potential WR and a reset potential V0 are supplied to the wiring VL1 in different periods. Similarly, a first data potential DG is supplied to the wiring SL2, and a second data potential WG and the reset potential V0 are supplied to the wiring VL2. A first data potential DB is supplied to the wiring SL3, and a second data potential WB and the reset potential V0 are supplied to the wiring VL3.

An example of a data writing operation will be described using the circuit 22 aR as an example. Note that the circuit 22 aG and the circuit 22 aB can also be driven by a similar method. For simplicity's sake, the following description will be made without consideration of the influence of the threshold voltage of each transistor, capacitance components of the transistors and the wirings, and the like.

First, the transistor M1, the transistor M3, and the transistor M4 are turned on, whereby the first data potential DR is supplied from the wiring SL1 and the reset potential V0 is supplied from the wiring VL1. Thus, the gate potential of the transistor M2 becomes the first data potential DR, and a voltage DR-V0 is stored in the capacitor C1 and the capacitor C3. Then, the transistor M1 and the transistor M3 are turned off and the transistor M4 is turned on, whereby the second data potential WR is supplied from the wiring VL1. At this time, the node to which the gate of the transistor M2 is connected is in a floating state; hence, the potential of the gate of the transistor M2 changes as the potential of the other electrode of the capacitor C3 changes from the reset potential V0 to the second data potential WR. For example, when the second data potential WR is higher than the reset potential V0, the potential of the gate of the transistor M2 increases.

In the above manner, the circuit 22 aR can generate the potential of the gate of the transistor M2 with the use of two data potentials. Similarly, the circuit 22 aG and the circuit 22 aB can generate the gate potential of the transistor M2 with the use of two data potentials.

When the first data potential DR and the reset potential V0 are supplied in the same period, the gate-source voltage of the transistor M2 can be determined regardless of the electrical characteristics of the light-emitting and light-receiving element or the light-emitting element. Thus, high-quality display is possible.

Note that each transistor may have a structure with a back gate. Although the example in which all the transistors each include a back gate is shown here, one embodiment of the present invention is not limited thereto, and a transistor that includes a back gate and a transistor that does not include a back gate may be used in combination.

Structure Example 3-2

The example where one pixel includes three subpixels is described above; an example where one pixel includes two subpixels will be described below.

FIG. 11A illustrates an example of method for arranging 3×3 pixels. FIG. 11A illustrates pixels in an i-th row and a j-th column (i and j are each independently an integer greater than or equal to 1) to an (i+2)th row and a (j+2)th column.

In FIG. 11A, the pixels 30G and the pixels 30B are alternately arranged in the row direction and the column direction. The pixel 30G includes the subpixel 20 aR and the subpixel 20 aG. The pixel 30B includes the subpixel 20 aR and the subpixel 20 aB.

For example, to the pixel 30G positioned in the i-th row and the j-th column, a wiring GL1[i], a wiring GL2[i], a wiring RS[i], and a wiring SE[i] that extend in the row direction and a wiring SL1[j], a wiring SL2[j], a wiring VL1[j], a wiring VL2[j], and a wiring WX[j] that extend in the column direction are connected.

Note that the subpixel 20R, the subpixel 20G, and the subpixel 20B shown in Structure example 2 above can alternatively be used instead of the subpixel 20 aR, the subpixel 20 aG, and the subpixel 20 aB. In that case, the wiring GL2, the wiring VL1, the wiring VL2, and the like are omitted.

FIG. 11B illustrates an example of a method for arranging the light-emitting and light-receiving elements MER, the light-emitting elements ELG, and the light-emitting elements ELB. The light-emitting and light-receiving elements MER are arranged at regular intervals in the row direction and the column direction. The light-emitting elements ELG and the light-emitting elements ELB are alternately arranged in the row direction and the column direction. The light-emitting and light-receiving element MER, the light-emitting element ELG, and the light-emitting element ELB have a shape such that a square is tilted at approximately 45 degrees with respect to the arrangement direction. This can increase the distance between adjacent elements; hence, when the light-emitting elements and the light-emitting and light-receiving elements are separately formed, they can be formed with high yield.

FIG. 12 illustrates an example of a circuit diagram of the pixel 30G in the i-th row and the j-th column and the pixel 30B in the (i+1)th row and the j-th column. Structure example 3-1 above can be referred to for the configurations of the subpixel 20 aR, the subpixel 20 aG, and the subpixel 20 aB.

[Driving Method Example]

An example of a method for driving the display device will be described below. Here, the description will be made using the structure shown in Structure example 3-2 above, in which one pixel includes two subpixels, as an example.

In the following description, the display device includes a display portion in which a plurality of pixels are arranged in a matrix of M rows and N columns (M and N are each independently an integer greater than or equal to 2).

FIG. 13 and FIG. 14 schematically show the operation of the display device. The operation of the display device is roughly divided into a period during which an image is displayed using the light-emitting elements and the light-emitting and light-receiving elements (a display period) and a period during which imaging is performed using the light-emitting and light-receiving elements (also referred to as sensors) (an imaging period). The display period is a period during which image data is written to pixels and display based on the image data is performed. The imaging period is a period during which image capturing with the light-emitting and light-receiving elements is performed and imaging data is read out.

First, the operation in the display period is described with reference to FIG. 13 .

In the display period, an operation of writing data to pixels is performed repeatedly. In the period, no sensor operation is performed (denoted as “blank”). Note that an imaging operation can be performed in the display period.

Image data for one frame is written by one writing operation. As shown in FIG. 13 , data is written to pixels sequentially from the first column to the M-th column by one writing operation (denoted as “write”).

FIG. 13 shows a timing chart for the operation of writing data in the i-th row and the (i+1)th row. Here, changes in the potentials of the wiring GL1[i], the wiring GL2[i], a wiring GL1[i+1], a wiring GL2[i+1], the wiring REN, the wiring SL1[j], the wiring VL1[j], the wiring SL2[j], and the wiring VL2[j] are shown. FIG. 12 can be referred to for connection relations between the wirings and the pixels.

A period of writing data to one row is divided into two periods. Specifically, there are a period during which the first data potential DR and the like are written (denoted as “video write”) and a period during which the second data potential WR and the like are written (denoted as “weight write”).

In the video writing (video write[i]) period in the i-th row, the wiring GL1[i], the wiring GL2[i], and the wiring REN are set to a high-level potential. A first data potential DR[i,j] is supplied to the wiring SL1[j], and a first data potential DG[i,j] is supplied to the wiring SL2[j]. The reset potential V0 is supplied to the wiring VL1[j] and the wiring VL2[j]. Thus, the first data potential DR[i,j] is written to the subpixel 20 aR in the pixel 30G in the i-th row and the j-th column, and the first data potential DG[i,j] is written to the subpixel 20 aG.

Then, in the weight write[i] period, the potential of the wiring GL1[i] becomes a low-level potential. A second data potential WR[i,j] is supplied to the wiring VL1[j], and a second data potential WG[i,j] is supplied to the wiring VL2[j]. Thus, a potential generated from the first data potential DR[i,j] and the second data potential WR[i,j] is written to the subpixel 20 aR[i,j] in the pixel 30G in the i-th row and the j-th column. Similarly, a potential generated from the first data potential DG[i,j] and the second data potential WG[i,j] is written to the subpixel 20 aG[i,j].

Thus, the operation of writing data in the i-th row is completed.

Next, the operation of writing data in the (i+1)th row is performed. Also in the (i+1)th row, by performing an operation similar to that in the i-th row, a potential generated from a first data potential DR[i+1,j] and a second data potential WR[i+1,j] is written to the subpixel 20 aR[i+1,j] in the pixel 30B in the (i+1)th row and the j-th column. Similarly, a potential generated from a first data potential DG[i+1,j] and a second data potential WG[i+1,j] is written to the subpixel 20 aB[i+1,j].

By thus providing the two periods, a video writing period and a weight writing period, two kinds of data can be written to each subpixel. Hence, grayscale correction, luminance correction, or the like can be performed. In addition, display with two kinds of images superimposed on each other can be easily performed.

Next, the operation in the imaging period is described with reference to FIG. 14 . The case of performing an imaging operation in a global shutter mode is described here. Note that without limitation to a global shutter mode, a driving method with a rolling shutter mode can also be employed.

The imaging period is divided into a period during which imaging is performed simultaneously in the pixels (this period is denoted as “imaging” and hereinafter also referred to as an imaging operation period to be distinguished from the imaging period) and a period during which imaging data is read out sequentially row by row (denoted as “readout”). The imaging operation period is divided into an initialization period, a light exposure period, and a transfer period. In the reading period, imaging data is read out from one row at a time from the first row to the M-th row.

FIG. 14 shows a timing chart in the imaging operation period and the reading period. Here, changes in the potentials of the wiring TX, the wiring SE[i], the wiring RS[i], a wiring SE[i+1], a wiring RS[i+1], wirings WX[1:N], wirings GL1[1:M], wirings GL2[1:M], the wiring REN, wirings SL[1:N], and wirings VL[1:N] are shown. Here, the wirings WX from the first column to the N-th column are collectively expressed as the wirings WX[1:N]. Similarly, the wirings GL1 are collectively expressed as the wirings GL[1:M], and the wirings GL2 are collectively expressed as the wirings GL[1:M]. The wirings SL1, the wirings SL2, and the like are collectively expressed as the wirings SL[1:N]; the wirings VL1, the wirings VL2, and the like are collectively expressed as the wirings VL[1:N].

In the initialization period, the wiring REN is set to a low-level potential. Thus, the transistor M10 is turned off in all the pixels.

By setting the wiring TX, the wiring RS[i], and the wiring RS[i+1] to a high-level potential, a predetermined potential is supplied from the wiring VRS to one of the light-emitting and light-receiving element MER and a node to which the gate of the transistor M13 is connected. Thus, the operation of resetting all the pixels is performed.

Then, in the light exposure period, the wiring TX, the wiring RS[i], and the wiring RS[i+1] are set to a low-level potential. Thus, electric charge is accumulated in the light-emitting and light-receiving element MER.

Next, in the transfer period, the wiring TX is set to a high-level potential. Thus, the electric charge accumulated in the light-emitting and light-receiving element MER can be transferred to the node to which the gate of the transistor M13 is connected. After that, setting the wiring TX to a low-level potential brings about a state where the potential of the node is held.

Then, imaging data is read out row by row. In the reading period, a high-level potential is sequentially supplied to a wiring SE[1] to a wiring SE[N], whereby data can be read out from all the pixels. For example, for reading in the i-th row, by setting the wiring SE[i] to a high-level potential, data DW[i] in the i-th row is output to the wirings WX[1:N]. Specifically, data DW[i,j] in the i-th row and the j-th column is output to one wiring WX[j].

Here, in the imaging period, a low-level potential is always supplied to the wiring REN. Accordingly, the light-emitting and light-receiving element MER and the transistor M2 are electrically insulated from each other particularly in the light exposure period and the transfer period. Consequently, noise is reduced, and imaging with high accuracy can be performed.

In the imaging period, each pixel is preferably set in a state of holding image data that is most recently written (denoted as “hold”). Thus, when the imaging period ends and the potential of the wiring REN changes from a low-level potential to a high-level potential, an image corresponding to the held image data can be displayed immediately. When image data written to the subpixel 20 aG or the subpixel 20 aB is held in the imaging period, crosstalk noise affecting the anode of the light-emitting and light-receiving element MER in the subpixel 20 aR can be reduced.

The above is the description of the driving method example.

At least part of the structure examples, the drawings corresponding thereto, and the like exemplified in this embodiment can be implemented in combination with the other structure examples, the other drawings, and the like as appropriate.

Embodiment 3

In this embodiment, display devices of embodiments of the present invention will be described with reference to FIG. 15 to FIG. 27 .

The display device of one embodiment of the present invention includes a light-emitting element and a light-emitting and light-receiving element.

The light-emitting and light-receiving element can be manufactured by combining an organic EL element and an organic photodiode, which are respectively a light-emitting element and a light-receiving element. For example, by adding an active layer of an organic photodiode to a layered structure of an organic EL element, the light-emitting and light-receiving element can be manufactured. Furthermore, in the light-emitting and light-receiving element formed of a combination of an organic EL element and an organic photodiode, concurrently depositing layers that can be shared with the organic EL element can inhibit an increase in the number of deposition steps.

For example, one of a pair of electrodes (a common electrode) can be a layer shared by the light-emitting and light-receiving element and the light-emitting element. For example, at least one of a hole-injection layer, a hole-transport layer, an electron-transport layer, and an electron-injection layer is preferably a layer shared by the light-emitting and light-receiving element and the light-emitting element. As another example, the light-emitting and light-receiving element and the light-emitting element can have the same structure except for the presence or absence of an active layer of the light-receiving element. That is, the light-emitting and light-receiving element can be manufactured by only adding the active layer of the light-receiving element to the light-emitting element. When the light-emitting and light-receiving element and the light-emitting element include common layers in such a manner, the number of deposition steps and the number of masks can be reduced, thereby reducing the number of manufacturing steps and the manufacturing cost of the display device. Furthermore, the display device including the light-emitting and light-receiving element can be manufactured using an existing manufacturing device and an existing manufacturing method for the display device.

Note that a layer included in the light-emitting and light-receiving element may have a different function between the case where the light-emitting and light-receiving element function as a light-receiving element and the case where the light-emitting and light-receiving element function as a light-emitting element. In this specification, the name of a component is based on its function in the case where the light-emitting and light-receiving element functions as a light-emitting element. For example, a hole-injection layer functions as a hole-injection layer in the case where the light-emitting and light-receiving element functions as a light-emitting element, and functions as a hole-transport layer in the case where the light-emitting and light-receiving element functions as a light-receiving element. Similarly, an electron-injection layer functions as an electron-injection layer in the case where the light-emitting and light-receiving element functions as a light-emitting element, and functions as an electron-transport layer in the case where the light-emitting and light-receiving element function as a light-receiving element.

As described above, the display device of this embodiment includes light-emitting and light-receiving elements and light-emitting elements in its display portion. Specifically, light-emitting and light-receiving elements and light-emitting elements are arranged in a matrix in the display portion. Accordingly, the display portion has one or both of an image capturing function and a sensing function in addition to a function of displaying an image.

The display portion can be used as an image sensor or a touch sensor. That is, by sensing light with the display portion, an image can be captured or an approach or touch of an object (e.g., a finger or a stylus) can be detected. Furthermore, in the display device of this embodiment, the light-emitting elements can be used as a light source for the sensor. Accordingly, a light-receiving portion and a light source do not need to be provided separately from the display device; hence, the number of components of an electronic device can be reduced.

In the display device of this embodiment, when an object reflects light emitted from the light-emitting element included in the display portion, the light-emitting and light-receiving element can sense the reflected light; thus, image capturing or touch (contact or approach) detection is possible even in a dark place.

The display device of this embodiment has a function of displaying images with the use of the light-emitting elements and the light-emitting and light-receiving elements. That is, the light-emitting elements and the light-emitting and light-receiving elements function as display elements.

As the light-emitting element, an EL element such as an OLED (Organic Light Emitting Diode) or a QLED (Quantum-dot Light Emitting Diode) is preferably used. Examples of a light-emitting substance contained in the EL element include a substance exhibiting fluorescence (a fluorescent material), a substance exhibiting phosphorescence (a phosphorescent material), an inorganic compound (such as a quantum dot material), and a substance exhibiting thermally activated delayed fluorescence (a thermally activated delayed fluorescence (TADF) material). Alternatively, an LED such as a micro-LED (Light Emitting Diode) can be used as the light-emitting element.

The display device of this embodiment has a function of detecting light with the use of the light-emitting and light-receiving elements. The light-emitting and light-receiving element can detect light having a shorter wavelength than light emitted by the light-emitting and light-receiving element itself.

When the light-emitting and light-receiving element is used as an image sensor, the display device of this embodiment can capture an image using the light-emitting and light-receiving element. For example, the display device of this embodiment can be used as a scanner.

For example, data on a fingerprint, a palm print, or the like can be obtained with the use of the image sensor. That is, a biological authentication sensor can be incorporated in the display device of this embodiment. When the display device incorporates a biological authentication sensor, the number of components of an electronic device can be reduced as compared to the case where a biological authentication sensor is provided separately from the display device; thus, the size and weight of the electronic device can be reduced.

Data on facial expression, eye movement, change of the pupil diameter, or the like of a user can be obtained with the use of the image sensor. By analysis of the data, information on the user's physical and mental state can be obtained. Changing the output contents of one or both of display and sound on the basis of the information allows the user to safely use a device for VR (Virtual Reality), a device for AR (Augmented Reality), or a device for MR (Mixed Reality), for example.

When the light-emitting and light-receiving element is used as a touch sensor, the display device of this embodiment can detect the approach or contact of an object with the use of the light-emitting and light-receiving element.

The light-emitting and light-receiving element functions as a photoelectric conversion element that detects light entering the light-emitting and light-receiving element and generates electric charge. The amount of generated electric charge depends on the amount of incident light.

The light-emitting and light-receiving element can be manufactured by adding an active layer of the light-receiving element to the above-described structure of the light-emitting element.

For the light-emitting and light-receiving element, an active layer of a pn photodiode or a pin photodiode can be used, for example.

It is particularly preferable to use, for the light-emitting and light-receiving element, an active layer of an organic photodiode including a layer containing an organic compound. An organic photodiode, which is easily made thin, lightweight, and large in area and has a high degree of freedom for shape and design, can be used in a variety of display devices.

FIG. 15A to FIG. 15D are cross-sectional views of display devices of embodiments of the present invention.

A display device 350A illustrated in FIG. 15A includes, between a substrate 351 and a substrate 359, a layer 353 including a light-emitting and light-receiving element and a layer 357 including light-emitting elements.

A display device 350B illustrated in FIG. 15B includes, between the substrate 351 and the substrate 359, the layer 353 including a light-emitting and light-receiving element, a layer 355 including transistors, and the layer 357 including light-emitting elements.

In the display device 350A and the display device 350B, green (G) light and blue (B) light are emitted from the layer 357 including light-emitting elements, and red (R) light is emitted from the layer 353 including a light-emitting and light-receiving element. In the display device of one embodiment of the present invention, the color of light emitted from the layer 353 including a light-emitting and light-receiving element is not limited to red.

The light-emitting and light-receiving element included in the layer 353 including the light-emitting and light-receiving element can detect light that enters from the outside of the display device 350A or the display device 350B. The light-emitting and light-receiving element can detect one or both of green (G) light and blue (B) light, for example.

The display device of one embodiment of the present invention includes a plurality of pixels arranged in a matrix. One pixel includes one or more subpixels. One subpixel includes one light-emitting and light-receiving element or one light-emitting element. For example, the pixel can have a structure including three subpixels (e.g., three colors of R, G, and B or three colors of yellow (Y), cyan (C), and magenta (M)) or four subpixels (e.g., four colors of R, G, B, and white (W) or four colors of R, G, B, and Y). The subpixel of at least one color includes a light-emitting and light-receiving element. The light-emitting and light-receiving element may be provided in all the pixels or may be provided in some of the pixels. In addition, one pixel may include a plurality of light-emitting and light-receiving elements.

The layer 355 including transistors includes a transistor electrically connected to the light-emitting and light-receiving element and a transistor electrically connected to the light-emitting element, for example. The layer 355 including transistors may also include a wiring, an electrode, a terminal, a capacitor, a resistor, or the like.

The display device of one embodiment of the present invention may have a function of detecting an object such as a finger that is touching the display device (FIG. 15C). Alternatively, the display device of one embodiment of the present invention may have a function of detecting an object that is approaching (but is not touching) the display device (FIG. 15D). For example, light emitted from the light-emitting element in the layer 357 including light-emitting elements is reflected by a finger 352 that touches or approaches the display device 350B as illustrated in FIG. 15C and FIG. 15D; then, the light-emitting and light-receiving element in the layer 353 including the light-emitting and light-receiving element detects the reflected light. Thus, the touch or approach of the finger 352 on/to the display device 350B can be detected.

[Pixel]

FIG. 15E to FIG. 15G and FIG. 16A to FIG. 16D illustrate examples of pixels. Note that the arrangement of subpixels is not limited to the illustrated order. For example, the positions of a subpixel (B) and a subpixel (G) may be reversed.

A pixel illustrated in FIG. 15E employs stripe arrangement and includes a subpixel (MER) that emits red light and has a light-receiving function, a subpixel (G) that emits green light, and a subpixel (B) that emits blue light. By using a light-emitting and light-receiving element instead of a light-emitting element in the R subpixel, a display device including a pixel composed of three subpixels of R, G, and B can have a light-receiving function in the pixel.

A pixel illustrated in FIG. 15F employs matrix arrangement and includes the subpixel (MER) that emits red light and has a light-receiving function, the subpixel (G) that emits green light, the subpixel (B) that emits blue light, and a subpixel (W) that emits white light. By using a light-emitting and light-receiving element instead of a light-emitting element in the R subpixel, a display device including a pixel composed of four subpixels of R, G, B, and W can also have a light-receiving function in the pixel.

Pixels illustrated in FIG. 15G employ PenTile arrangement and each include subpixels emitting light of two colors that differ among the pixels. The upper left pixel and the lower right pixel in FIG. 15G each include the subpixel (MER) that emits red light and has a light-receiving function and the subpixel (G) that emits green light. The lower left pixel and the upper right pixel in FIG. 15G each include the subpixel (G) that emits green light and the subpixel (B) that emits blue light. Note that the shape of the subpixels illustrated in FIG. 15G indicates a top surface shape of the light-emitting element or the light-emitting and light-receiving element included in the subpixels.

A pixel illustrated in FIG. 16A includes the subpixel (MER) that emits red light and has a light-receiving function, the subpixel (G) that emits green light, and the subpixel (B) that emits blue light. The subpixel (MER) is provided in a column different from a column where the subpixel (G) and the subpixel (B) are positioned. The subpixel (G) and the subpixel (B) are alternately arranged in the same column; one is provided in an odd-numbered row and the other is provided in an even-numbered row. Note that the color of the subpixel positioned in a column different from the column where the subpixels of the other colors are positioned is not limited to red (R) and may alternatively be green (G) or blue (B).

FIG. 16B illustrates two pixels, and one pixel is composed of three subpixels surrounded by dotted lines. The pixel illustrated in FIG. 16B includes the subpixel (MER) that emits red light and has a light-receiving function, the subpixel (G) that emits green light, and the subpixel (B) that emits blue light. In the pixel on the left in FIG. 16B, the subpixel (G) is positioned in the same row as the subpixel (MER), and the subpixel (B) is positioned in the same column as the subpixel (MER). In the pixel on the right in FIG. 16B, the subpixel (G) is positioned in the same row as the subpixel (MER), and the subpixel (B) is positioned in the same column as the subpixel (G). In the pixel layout illustrated in FIG. 16B, the subpixel (MER), the subpixel (G), and the subpixel (B) are repeatedly arranged in both the odd-numbered row and the even-numbered row. In addition, subpixels of different colors are arranged in the odd-numbered row and the even-numbered row in every column.

FIG. 16C is a modification example of the pixel arrangement of FIG. 15G. The upper left pixel and the lower right pixel in FIG. 16C each include the subpixel (MER) that emits red light and has a light-receiving function and the subpixel (G) that emits green light. The lower left pixel and the upper right pixel in FIG. 16C each include the subpixel (MER) that emits red light and has a light-receiving function and the subpixel (B) that emits blue light.

In FIG. 15G, the subpixel (G) that emits green light is provided in each pixel. Meanwhile, in FIG. 16C, the subpixel (MER) that emits red light and has a light-receiving function is provided in each pixel. The structure illustrated in FIG. 16C achieves higher-resolution image capturing than the structure illustrated in FIG. 15G because the subpixel having a light-receiving function is provided in each pixel. Thus, the accuracy of biometric authentication can be increased, for example.

The top surface shape of the light-emitting elements and the light-emitting and light-receiving elements is not particularly limited and can be a circular shape, an elliptical shape, a polygonal shape, a polygonal shape with rounded corners, or the like. The top surface shape of the light-emitting elements included in the subpixels (G) is circular in the example in FIG. 15G and square in the example in FIG. 16C. The top surface shape of the light-emitting elements and the light-emitting and light-receiving elements may vary depending on the color thereof, or the light-emitting elements and the light-emitting and light-receiving elements of some colors or every color may have the same top surface shape.

The aperture ratio of subpixels may vary depending on the color thereof, or may be the same among the subpixels of some colors or all colors. For example, the aperture ratio of a subpixel provided in each pixel (the subpixel (G) in FIG. 15G, and the subpixel (MER) in FIG. 16C) may be made lower than that of a subpixel of another color.

FIG. 16D is a modification example of the pixel arrangement of FIG. 16C. Specifically, the structure of FIG. 16D is obtained by rotating the structure of FIG. 16C by 45°. Although one pixel is regarded as being composed of two subpixels in FIG. 16C, one pixel can be regarded as being composed of four subpixels as illustrated in FIG. 16D.

In the description with reference to FIG. 16D, one pixel is regarded as being composed of four subpixels surrounded by dotted lines. One pixel includes two subpixels (MER), one subpixel (G), and one subpixel (B). The pixel including a plurality of subpixels having a light-receiving function allows high-resolution image capturing. Accordingly, the accuracy of biometric authentication can be increased. For example, the resolution of image capturing can be the square root of 2 times the resolution of display.

A display device that employs the structure illustrated in FIG. 16C or FIG. 16D includes p first light-emitting elements (p is an integer greater than or equal to 2), q second light-emitting elements (q is an integer greater than or equal to 2), and r light-emitting and light-receiving elements (r is an integer greater than p and greater than q). As for p and r, r=2p is satisfied. As for p, q, and r, r=p+q is satisfied. Either the first light-emitting elements or the second light-emitting elements emits green light, and the other light-emitting elements emit blue light. The light-emitting and light-receiving elements emit red light and have a light-receiving function.

In the case where touch detection is performed with the light-emitting and light-receiving elements, for example, it is preferable that light emitted from a light source be hard for a user to recognize. Since blue light has low visibility than green light, light-emitting elements that emit blue light are preferably used as a light source. Accordingly, the light-emitting and light-receiving elements preferably have a function of receiving blue light.

As described above, the display device of one embodiment of the present invention can employ pixels with a variety of arrangements.

The pixel arrangement in the display device of this embodiment need not be changed when a light-receiving function is incorporated into pixels; thus, the display portion can be provided with one or both of an image capturing function and a sensing function without a reduction in the aperture ratio or resolution.

[Light-Emitting and Light-Receiving Element]

FIG. 17A to FIG. 17E illustrate examples of layered structures of light-emitting and light-receiving elements.

The light-emitting and light-receiving element includes at least an active layer and a light-emitting layer between a pair of electrodes.

In addition to the active layer and the light-emitting layer, the light-emitting and light-receiving element may further include a layer containing a substance with a high hole-injection property, a substance with a high hole-transport property, a substance with a high hole-blocking property, a substance with a high electron-transport property, a substance with a high electron-injection property, a substance with a high electron-blocking property, a substance with a bipolar property (a substance with high electron- and hole-transport properties), or the like.

The light-emitting and light-receiving elements illustrated in FIG. 17A to FIG. 17C each include a first electrode 180, a hole-injection layer 181, a hole-transport layer 182, an active layer 183, a light-emitting layer 193, an electron-transport layer 184, an electron-injection layer 185, and a second electrode 189.

Note that each of the light-emitting and light-receiving elements illustrated in FIG. 17A to FIG. 17C can be regarded as having a structure where the active layer 183 is added to a light-emitting element. Therefore, the light-emitting and light-receiving element can be formed concurrently with the formation of the light-emitting element only by adding a step of depositing the active layer 183 in the manufacturing process of the light-emitting element. The light-emitting element and the light-emitting and light-receiving element can be formed over one substrate. Thus, the display portion can be provided with one or both of an image capturing function and a sensing function without a significant increase in the number of manufacturing steps.

The stacking order of the light-emitting layer 193 and the active layer 183 is not limited. FIG. 17A illustrates an example in which the active layer 183 is provided over the hole-transport layer 182 and the light-emitting layer 193 is provided over the active layer 183. FIG. 17B illustrates an example in which the light-emitting layer 193 is provided over the hole-transport layer 182 and the active layer 183 is provided over the light-emitting layer 193. The active layer 183 and the light-emitting layer 193 may be in contact with each other as illustrated in FIG. 17A and FIG. 17B.

As illustrated in FIG. 17C, a buffer layer is preferably provided between the active layer 183 and the light-emitting layer 193. As the buffer layer, at least one layer of a hole-injection layer, a hole-transport layer, an electron-transport layer, an electron-injection layer, a hole-blocking layer, an electron-blocking layer, and the like can be used. FIG. 17C illustrates an example in which the hole-transport layer 182 is used as the buffer layer.

The buffer layer provided between the active layer 183 and the light-emitting layer 193 can inhibit transfer of excitation energy from the light-emitting layer 193 to the active layer 183. Furthermore, the buffer layer can also be used to adjust the optical path length (cavity length) of the microcavity structure. Thus, high emission efficiency can be obtained from the light-emitting and light-receiving element including the buffer layer between the active layer 183 and the light-emitting layer 193.

The light-emitting and light-receiving element illustrated in FIG. 17D is different from the light-emitting and light-receiving elements illustrated in FIG. 17A and FIG. 17C in not including the hole-transport layer 182. The light-emitting and light-receiving element may exclude at least one of the hole-injection layer 181, the hole-transport layer 182, the electron-transport layer 184, and the electron-injection layer 185. Furthermore, the light-emitting and light-receiving element may include another functional layer such as a hole-blocking layer or an electron-blocking layer.

The light-emitting and light-receiving element illustrated in FIG. 17E is different from the light-emitting and light-receiving elements illustrated in FIG. 17A to FIG. 17C in including a layer 186 serving as both a light-emitting layer and an active layer instead of including the active layer 183 and the light-emitting layer 193.

As the layer 186 serving as both a light-emitting layer and an active layer, it is possible to use, for example, a layer containing three materials which are an n-type semiconductor that can be used for the active layer 183, a p-type semiconductor that can be used for the active layer 183, and a light-emitting substance that can be used for the light-emitting layer 193.

Note that an absorption band on the lowest energy side of an absorption spectrum of a mixed material of the n-type semiconductor and the p-type semiconductor and a maximum peak of an emission spectrum (PL spectrum) of the light-emitting substance preferably do not overlap each other and are further preferably positioned fully apart from each other.

In the light-emitting and light-receiving element, a conductive film that transmits visible light is used as the electrode through which light is extracted. A conductive film that reflects visible light is preferably used as the electrode through which light is not extracted.

When the light-emitting and light-receiving element is driven as a light-emitting element, the hole-injection layer serves as a layer that injects holes from the anode to the light-emitting and light-receiving element. The hole-injection layer is a layer containing a material with a high hole-injection property. As the material with a high hole-injection property, it is possible to use an aromatic amine compound or a composite material containing a hole-transport material and an acceptor material (electron-accepting material).

When the light-emitting and light-receiving element is driven as alight-emitting element, the hole-transport layer serves as a layer that transports holes injected from the anode by the hole-injection layer, to the light-emitting layer. When the light-emitting and light-receiving element is driven as a light-receiving element, the hole-transport layer serves as a layer that transports holes generated in the active layer on the basis of incident light, to the anode. The hole-transport layer is a layer containing a hole-transport material. As the hole-transport material, a substance having a hole mobility greater than or equal to 10−6 cm2/Vs is preferable. Note that other substances can also be used as long as they have a property of transporting more holes than electrons. As the hole-transport material, a material having a high hole-transport property, such as a π-electron-rich heteroaromatic compound (e.g., a carbazole derivative, a thiophene derivative, and a furan derivative) or an aromatic amine (a compound having an aromatic amine skeleton), is preferable.

When the light-emitting and light-receiving element is driven as a light-emitting element, the electron-transport layer serves as a layer that transports electrons injected from the cathode by the electron-injection layer, to the light-emitting layer. When the light-emitting and light-receiving element is driven as a light-receiving element, the electron-transport layer serves as a layer that transports electrons generated in the active layer on the basis of incident light, to the cathode. The electron-transport layer is a layer containing an electron-transport material. As the electron-transport material, a substance with an electron mobility greater than or equal to 1×10−6 cm2/Vs is preferable. Note that other substances can also be used as long as they have a property of transporting more electrons than holes. As the electron-transport material, it is possible to use a material having a high electron-transport property, such as a metal complex having a quinoline skeleton, a metal complex having a benzoquinoline skeleton, a metal complex having an oxazole skeleton, a metal complex having a thiazole skeleton, an oxadiazole derivative, a triazole derivative, an imidazole derivative, an oxazole derivative, a thiazole derivative, a phenanthroline derivative, a quinoline derivative having a quinoline ligand, a benzoquinoline derivative, a quinoxaline derivative, a dibenzoquinoxaline derivative, a pyridine derivative, a bipyridine derivative, a pyrimidine derivative, or a π-electron deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound.

When the light-emitting and light-receiving element is driven as a light-emitting element, the electron-injection layer serves as a layer that injects electrons from the cathode to the light-emitting and light-receiving element. The electron-injection layer is a layer containing a material with a high electron-injection property. As the material with a high electron-injection property, an alkali metal, an alkaline earth metal, or a compound thereof can be used. As the material with a high electron-injection property, a composite material containing an electron-transport material and a donor material (electron-donating material) can also be used.

The light-emitting layer 193 is a layer that contains a light-emitting substance. The light-emitting layer 193 can contain one or more kinds of light-emitting substances. As the light-emitting substance, a substance that exhibits an emission color of blue, purple, bluish purple, green, yellowish green, yellow, orange, red, or the like is appropriately used. As the light-emitting substance, a substance that emits near-infrared light can also be used.

Examples of the light-emitting substance include a fluorescent material, a phosphorescent material, a TADF material, and a quantum dot material.

Examples of the fluorescent material include a pyrene derivative, an anthracene derivative, a triphenylene derivative, a fluorene derivative, a carbazole derivative, a dibenzothiophene derivative, a dibenzofuran derivative, a dibenzoquinoxaline derivative, a quinoxaline derivative, a pyridine derivative, a pyrimidine derivative, a phenanthrene derivative, and a naphthalene derivative.

Examples of the phosphorescent material include an organometallic complex (particularly an iridium complex) having a 4H-triazole skeleton, a 1H-triazole skeleton, an imidazole skeleton, a pyrimidine skeleton, a pyrazine skeleton, or a pyridine skeleton; an organometallic complex (particularly an iridium complex) having a phenylpyridine derivative including an electron-withdrawing group as a ligand; a platinum complex; and a rare earth metal complex.

The light-emitting layer 193 may contain one or more kinds of organic compounds (e.g., a host material and an assist material) in addition to the light-emitting substance (guest material). As one or more kinds of organic compounds, one or both of the hole-transport material and the electron-transport material can be used. Alternatively, as one or more kinds of organic compounds, a bipolar material or a TADF material may be used.

The light-emitting layer 193 preferably contains a phosphorescent material and a combination of a hole-transport material and an electron-transport material that easily forms an exciplex. With such a structure, light emission can be efficiently obtained by ExTET (Exciplex-Triplet Energy Transfer), which is energy transfer from an exciplex to a light-emitting substance (a phosphorescent material). When a combination of materials is selected so as to form an exciplex that exhibits light emission whose wavelength overlaps the wavelength of a lowest-energy-side absorption band of the light-emitting substance, energy can be transferred smoothly and light emission can be obtained efficiently. With this structure, high efficiency, low-voltage driving, and a long lifetime of the light-emitting element can be achieved at the same time.

In the combination of materials for forming an exciplex, the HOMO level (highest occupied molecular orbital level) of the hole-transport material is preferably higher than or equal to the HOMO level of the electron-transport material. The LUMO level (lowest unoccupied molecular orbital level) of the hole-transport material is preferably higher than or equal to the LUMO level of the electron-transport material. The LUMO levels and the HOMO levels of the materials can be derived from the electrochemical characteristics (reduction potentials and oxidation potentials) of the materials that are measured by cyclic voltammetry (CV).

Note that the formation of an exciplex can be confirmed by a phenomenon in which the emission spectrum of a mixed film in which the hole-transport material and the electron-transport material are mixed is shifted to the longer wavelength side than the emission spectrum of each of the materials (or has another peak on the longer wavelength side), observed by comparison of the emission spectra of the hole-transport material, the electron-transport material, and the mixed film of these materials, for example. Alternatively, the formation of an exciplex can be confirmed by a difference in transient response, such as a phenomenon in which the transient photoluminescence (PL) lifetime of the mixed film has longer lifetime components or has a larger proportion of delayed components than that of each of the materials, observed by comparison of the transient PL of the hole-transport material, the transient PL of the electron-transport material, and the transient PL of the mixed film of these materials. The transient PL can be rephrased as transient electroluminescence (EL). That is, the formation of an exciplex can also be confirmed by a difference in transient response observed by comparison of the transient EL of the hole-transport material, the transient EL of the electron-transport material, and the transient EL of the mixed film of these materials.

The active layer 183 contains a semiconductor. Examples of the semiconductor include an inorganic semiconductor such as silicon and an organic semiconductor including an organic compound. This embodiment shows an example in which an organic semiconductor is used as the semiconductor included in the active layer. The use of an organic semiconductor is preferable because the light-emitting layer 193 and the active layer 183 can be formed by the same method (e.g., a vacuum evaporation method) and thus the same manufacturing device can be used.

Examples of an n-type semiconductor material contained in the active layer 183 are electron-accepting organic semiconductor materials such as fullerene (e.g., C60 and C70) and fullerene derivatives. Fullerene has a soccer ball-like shape, which is energetically stable. Both the HOMO level and the LUMO level of fullerene are deep (low). Having a deep LUMO level, fullerene has an extremely high electron-accepting property (acceptor property). When π-electron conjugation (resonance) spreads in a plane as in benzene, the electron-donating property (donor property) usually increases. However, since fullerene has a spherical shape, fullerene has a high electron-accepting property even when π-electrons widely spread. The high electron-accepting property efficiently causes rapid charge separation and is useful for a light-receiving element. Both C60 and C70 have a wide absorption band in the visible light region, and C70 is especially preferable because of having a larger π-electron conjugation system and a wider absorption band in the long wavelength region than C60.

Examples of the n-type semiconductor material include a metal complex having a quinoline skeleton, a metal complex having a benzoquinoline skeleton, a metal complex having an oxazole skeleton, a metal complex having a thiazole skeleton, an oxadiazole derivative, a triazole derivative, an imidazole derivative, an oxazole derivative, a thiazole derivative, a phenanthroline derivative, a quinoline derivative, a benzoquinoline derivative, a quinoxaline derivative, a dibenzoquinoxaline derivative, a pyridine derivative, a bipyridine derivative, a pyrimidine derivative, a naphthalene derivative, an anthracene derivative, a coumarin derivative, a rhodamine derivative, a triazine derivative, and a quinone derivative.

Examples of the p-type semiconductor material contained in the active layer 183 include electron-donating organic semiconductor materials such as copper(II) phthalocyanine (CuPc), tetraphenyldibenzoperiflanthene (DBP), zinc phthalocyanine (ZnPc), tin phthalocyanine (SnPc), and quinacridone.

Examples of the p-type semiconductor material include a carbazole derivative, a thiophene derivative, a furan derivative, and a compound having an aromatic amine skeleton. Other examples of the p-type semiconductor material include a naphthalene derivative, an anthracene derivative, a pyrene derivative, a triphenylene derivative, a fluorene derivative, a pyrrole derivative, a benzofuran derivative, a benzothiophene derivative, an indole derivative, a dibenzofuran derivative, a dibenzothiophene derivative, an indolocarbazole derivative, a porphyrin derivative, a phthalocyanine derivative, a naphthalocyanine derivative, a quinacridone derivative, a polyphenylene vinylene derivative, a polyparaphenylene derivative, a polyfluorene derivative, a polyvinylcarbazole derivative, and a polythiophene derivative.

The HOMO level of the electron-donating organic semiconductor material is preferably shallower (higher) than the HOMO level of the electron-accepting organic semiconductor material. The LUMO level of the electron-donating organic semiconductor material is preferably shallower (higher) than the LUMO level of the electron-accepting organic semiconductor material.

Fullerene having a spherical shape is preferably used as the electron-accepting organic semiconductor material, and an organic semiconductor material having a substantially planar shape is preferably used as the electron-donating organic semiconductor material. Molecules of similar shapes tend to aggregate, and aggregated molecules of similar kinds, which have molecular orbital energy levels close to each other, can improve the carrier-transport property.

For example, the active layer 183 is preferably formed by co-evaporation of an n-type semiconductor and a p-type semiconductor.

The layer 186 serving as both a light-emitting layer and an active layer is preferably formed using the above-described light-emitting material, n-type semiconductor, and p-type semiconductor.

The hole-injection layer 181, the hole-transport layer 182, the active layer 183, the light-emitting layer 193, the electron-transport layer 184, the electron-injection layer 185, and the layer 186 serving as both a light-emitting layer and an active layer may be formed using either a low-molecular compound or a high-molecular compound and may contain an inorganic compound. Each of the layers can be formed by an evaporation method (including a vacuum evaporation method), a transfer method, a printing method, an inkjet method, a coating method, or the like.

Detailed structures of the light-emitting and light-receiving element and the light-emitting elements included in the display device of one embodiment of the present invention will be described below with reference to FIG. 18 to FIG. 20 .

The display device of one embodiment of the present invention can have any of the following structures: a top-emission structure in which light is emitted in a direction opposite to the substrate where the light-emitting elements are formed, a bottom-emission structure in which light is emitted toward the substrate where the light-emitting elements are formed, and a dual-emission structure in which light is emitted toward both surfaces.

FIG. 18 to FIG. 20 illustrate top-emission display devices as examples.

Structure Example 4

The display device illustrated in FIG. 18A and FIG. 18B includes a light-emitting element 347B that emits blue (B) light, a light-emitting element 347G that emits green (G) light, and a light-emitting and light-receiving element 347MER that emits red (R) light and has a light-receiving function over a substrate 151 with the layer 355 including transistors therebetween.

FIG. 18A shows the case where the light-emitting and light-receiving element 347MER functions as alight-emitting element. FIG. 18A illustrates an example in which the light-emitting element 347B emits blue light, the light-emitting element 347G emits green light, and the light-emitting and light-receiving element 347MER emits red light.

FIG. 18B shows the case where the light-emitting and light-receiving element 347MER functions as a light-receiving element. FIG. 18B illustrates an example in which the light-emitting and light-receiving element 347MER detects blue light emitted by the light-emitting element 347B and green light emitted by the light-emitting element 347G.

The light-emitting element 347B, the light-emitting element 347G, and the light-emitting and light-receiving element 347MER each include a pixel electrode 191 and a common electrode 115. In this embodiment, the case where the pixel electrode 191 functions as an anode and the common electrode 115 functions as a cathode is described as an example.

In the description in this embodiment, also in the light-emitting and light-receiving element 347MER, the pixel electrode 191 functions as an anode and the common electrode 115 functions as a cathode as in the light-emitting elements. In other words, when the light-emitting and light-receiving element 347MER is driven by application of reverse bias between the pixel electrode 191 and the common electrode 115, light entering the light-emitting and light-receiving element 347MER can be detected and electric charge can be generated and extracted as current.

The common electrode 115 is shared by the light-emitting element 347B, the light-emitting element 347G, and the light-emitting and light-receiving element 347MER.

The material, thickness, and the like of the pair of electrodes can be the same in the light-emitting element 347B, the light-emitting element 347G, and the light-emitting and light-receiving element 347MER. Accordingly, the manufacturing cost of the display device can be reduced, and the manufacturing process of the display device can be simplified.

The structure of the display device illustrated in FIG. 18A and FIG. 18B will be specifically described.

The light-emitting element 347B includes a buffer layer 192B, a light-emitting layer 193B, and a buffer layer 194B in this order over the pixel electrode 191. The light-emitting layer 193B contains a light-emitting substance that emits blue light. The light-emitting element 347B has a function of emitting blue light.

The light-emitting element 347G includes a buffer layer 192G, a light-emitting layer 193G, and a buffer layer 194G in this order over the pixel electrode 191. The light-emitting layer 193G contains alight-emitting substance that emits green light. The light-emitting element 347G has a function of emitting green light.

The light-emitting and light-receiving element 347MER includes a buffer layer 192R, the active layer 183, a light-emitting layer 193R, and a buffer layer 194R in this order over the pixel electrode 191. The light-emitting layer 193R contains alight-emitting substance that emits red light. The active layer 183 contains an organic compound that absorbs light having a shorter wavelength than red light (e.g., one or both of green light and blue light). Note that an organic compound that absorbs ultraviolet light as well as visible light may be used for the active layer 183. The light-emitting and light-receiving element 347MER has a function of emitting red light. The light-emitting and light-receiving element 347MER has a function of detecting light emitted from at least one of the light-emitting element 347G and the light-emitting element 347B and preferably has a function of detecting light emitted from both of them.

The active layer 183 preferably contains an organic compound that does not easily absorb red light and absorbs light having a shorter wavelength than red light. Thus, the light-emitting and light-receiving element 347MER can have a function of efficiently emitting red light and a function of accurately detecting light having a shorter wavelength than red light.

The pixel electrode 191, the buffer layer 192R, the buffer layer 192G, the buffer layer 192B, the active layer 183, the light-emitting layer 193R, the light-emitting layer 193G, the light-emitting layer 193B, the buffer layer 194R, the buffer layer 194G, the buffer layer 194B, and the common electrode 115 may each have a single-layer structure or a stacked-layer structure.

In the display device illustrated in FIG. 18A and FIG. 18B, the buffer layer, the active layer, and the light-emitting layer are formed in each element individually.

The buffer layers 192R, 192G, and 192B can each include one or both of a hole-injection layer and a hole-transport layer. Furthermore, the buffer layers 192R, 192G, and 192B may each include an electron-blocking layer. The buffer layers 194B, 194G, and 194R can each include one or both of an electron-injection layer and an electron-transport layer. Furthermore, the buffer layers 194R, 194G, and 194B may each include a hole-blocking layer. Note that the above description of the layers included in the light-emitting and light-receiving element can be referred to for materials and the like of the layers included in the light-emitting elements. Note that the buffer layers 192R, 192G, and 192B are collectively referred to as a buffer layer 192 in some cases. The buffer layers 194B, 194G, and 194R are collectively referred to as a buffer layer 194 in some cases.

Structure Example 5

As illustrated in FIG. 19A and FIG. 19B, the light-emitting element 347B, the light-emitting element 347G, and the light-emitting and light-receiving element 347MER may include common layers between the pair of electrodes. Thus, the light-emitting and light-receiving element can be incorporated into the display device without a significant increase in the number of manufacturing steps.

The light-emitting element 347B, the light-emitting element 347G, and the light-emitting and light-receiving element 347MER illustrated in FIG. 19A include a common layer 112 and a common layer 114 in addition to the components illustrated in FIG. 18A and FIG. 18B.

The light-emitting element 347B, the light-emitting element 347G, and the light-emitting and light-receiving element 347MER illustrated in FIG. 19B are different from those illustrated in FIG. 18A and FIG. 18B in that the buffer layers 192R, 192G, and 192B and the buffer layers 194R, 194G, and 194B are not included and the common layer 112 and the common layer 114 are included.

The common layer 112 can include one or both of a hole-injection layer and a hole-transport layer. The common layer 114 can include one or both of an electron-injection layer and an electron-transport layer.

The common layer 112 and the common layer 114 may each have a single-layer structure or a stacked-layer structure.

Structure Example 6

The display device illustrated in FIG. 20A is an example in which the light-emitting and light-receiving element 347MER employs the layered structure illustrated in FIG. 17C.

The light-emitting and light-receiving element 347MER includes the hole-injection layer 181, the active layer 183, a hole-transport layer 182R, the light-emitting layer 193R, the electron-transport layer 184, the electron-injection layer 185, and the common electrode 115 in this order over the pixel electrode 191.

The hole-injection layer 181, the electron-transport layer 184, the electron-injection layer 185, and the common electrode 115 are common layers to the light-emitting element 347G and the light-emitting element 347B.

The light-emitting element 347G includes the hole-injection layer 181, a hole-transport layer 182G, the light-emitting layer 193G, the electron-transport layer 184, the electron-injection layer 185, and the common electrode 115 in this order over the pixel electrode 191.

The light-emitting element 347B includes the hole-injection layer 181, a hole-transport layer 182B, the light-emitting layer 193B, the electron-transport layer 184, the electron-injection layer 185, and the common electrode 115 in this order over the pixel electrode 191.

The light-emitting elements included in the display device of this embodiment preferably employs a microcavity structure. Thus, one of the pair of electrodes of the light-emitting elements is preferably an electrode having properties of transmitting and reflecting visible light (a semi-transmissive and semi-reflective electrode), and the other is preferably an electrode having a property of reflecting visible light (a reflective electrode). When the light-emitting elements have a microcavity structure, light obtained from the light-emitting layers can be resonated between both of the electrodes, whereby light emitted from the light-emitting elements can be intensified.

Note that the semi-transmissive and semi-reflective electrode can have a stacked-layer structure of a reflective electrode and an electrode having a property of transmitting visible light (also referred to as a transparent electrode). In this specification and the like, a reflective electrode functioning as part of a semi-transmissive and semi-reflective electrode may be referred to as a pixel electrode or a common electrode, and a transparent electrode may be referred to as an optical adjustment layer; however, in some cases, a transparent electrode (optical adjustment layer) can also be regarded as having a function of a pixel electrode or a common electrode.

The transparent electrode has a light transmittance higher than or equal to 40%. For example, an electrode whose transmittance for visible light (light with a wavelength greater than or equal to 400 nm and less than 750 nm) and near-infrared light (light with a wavelength greater than or equal to 750 nm and less than or equal to 1300 nm) is greater than or equal to 40% is preferably used in the light-emitting element. The reflectance of the semi-transmissive and semi-reflective electrode for visible light and near-infrared light is greater than or equal to 10% and less than or equal to 95%, preferably greater than or equal to 30% and less than or equal to 80%. The reflectance of the reflective electrode for visible light and near-infrared light is greater than or equal to 40% and less than or equal to 100%, preferably greater than or equal to 70% and less than or equal to 100%. These electrodes preferably have a resistivity of 1×10−2 Ωcm or lower.

The hole-transport layers 182B, 182G, and 182R may each have a function of an optical adjustment layer. Specifically, the thickness of the hole-transport layer 182B is preferably adjusted such that the optical distance between the pair of electrodes in the light-emitting element 347B intensifies blue light. Similarly, the thickness of the hole-transport layer 182G is preferably adjusted such that the optical distance between the pair of electrodes in the light-emitting element 347G intensifies green light. The thickness of the hole-transport layer 182R is preferably adjusted such that the optical distance between the pair of electrodes in the light-emitting and light-receiving element 347MER intensifies red light. The layer used as the optical adjustment layer is not limited to the hole-transport layer. Note that when the semi-transmissive and semi-reflective electrode has a stacked-layer structure of a reflective electrode and a transparent electrode, the optical distance between the pair of electrodes represents the optical distance between a pair of reflective electrodes.

Structure Example 7

The display device illustrated in FIG. 20B is an example in which the light-emitting and light-receiving element 347MER employs the layered structure illustrated in FIG. 17D.

The light-emitting and light-receiving element 347MER includes the hole-injection layer 181, the active layer 183, the light-emitting layer 193R, the electron-transport layer 184, the electron-injection layer 185, and the common electrode 115 in this order over the pixel electrode 191.

The hole-injection layer 181, the electron-transport layer 184, the electron-injection layer 185, and the common electrode 115 are common layers to the light-emitting element 347G and the light-emitting element 347B.

The light-emitting element 347G includes the hole-injection layer 181, the hole-transport layer 182G, the light-emitting layer 193G, the electron-transport layer 184, the electron-injection layer 185, and the common electrode 115 in this order over the pixel electrode 191.

The light-emitting element 347B includes the hole-injection layer 181, the hole-transport layer 182B, the light-emitting layer 193B, the electron-transport layer 184, the electron-injection layer 185, and the common electrode 115 in this order over the pixel electrode 191.

The hole-transport layer is provided in the light-emitting element 347G and the light-emitting element 347B and is not provided in the light-emitting and light-receiving element 347MER. In this manner, a layer provided in only one of the light-emitting elements and the light-emitting and light-receiving element may exist in addition to the active layer and the light-emitting layer.

A detailed structure of the display device of one embodiment of the present invention will be described below with reference to FIG. 21 to FIG. 26 .

[Display Device 310A]

FIG. 21A and FIG. 21B are cross-sectional views of a display device 310A.

The display device 310A includes a light-emitting element 190B, a light-emitting element 190G, and a light-emitting and light-receiving element 190MER.

The light-emitting element 190B includes the pixel electrode 191, the buffer layer 192B, the light-emitting layer 193B, the buffer layer 194B, and the common electrode 115. The light-emitting element 190B has a function of emitting blue light 321B.

The light-emitting element 190G includes the pixel electrode 191, the buffer layer 192G, the light-emitting layer 193G, the buffer layer 194G, and the common electrode 115. The light-emitting element 190G has a function of emitting green light 321G.

The light-emitting and light-receiving element 190MER includes the pixel electrode 191, the buffer layer 192R, the active layer 183, the light-emitting layer 193R, the buffer layer 194R, and the common electrode 115. The light-emitting and light-receiving element 190MER has a function of emitting red light 321R and a function of detecting light 322.

FIG. 21A shows the case where the light-emitting and light-receiving element 190MER functions as a light-emitting element. FIG. 21A illustrates an example in which the light-emitting element 190B emits blue light, the light-emitting element 190G emits green light, and the light-emitting and light-receiving element 190MER emits red light.

FIG. 21B shows the case where the light-emitting and light-receiving element 190MER functions as a light-receiving element. FIG. 21B illustrates an example in which the light-emitting and light-receiving element 190MER detects blue light emitted by the light-emitting element 190B and green light emitted by the light-emitting element 190G.

The pixel electrode 191 is positioned over an insulating layer 214. An end portion of the pixel electrode 191 is covered with a partition 216. Two adjacent pixel electrodes 191 are electrically insulated (electrically isolated) from each other by the partition 216.

An organic insulating film is suitable for the partition 216. Examples of materials that can be used for the organic insulating film include an acrylic resin, a polyimide resin, an epoxy resin, a polyamide resin, a polyimide-amide resin, a siloxane resin, a benzocyclobutene-based resin, a phenol resin, and precursors of these resins. The partition 216 is a layer that transmits visible light. Although the details will be described later, a partition that blocks visible light may be provided in place of the partition 216.

The display device 310A includes the light-emitting and light-receiving element 190MER, the light-emitting element 190G, the light-emitting element 190B, a transistor 342, and the like between a pair of substrates (the substrate 151 and a substrate 152).

The light-emitting and light-receiving element 190MER has a function of detecting light. Specifically, the light-emitting and light-receiving element 190MER is a photoelectric conversion element that receives the light 322 incident from the outside of the display device 310A and converts it into an electric signal. The light 322 can also be referred to as light that is emitted from one or both of the light-emitting element 190G and the light-emitting element 190B and then reflected by an object. The light 322 may enter the light-emitting and light-receiving element 190MER through a lens.

The light-emitting element 190G and the light-emitting element 190B have a function of emitting visible light. Specifically, the light-emitting element 190G and the light-emitting element 190B are each an electroluminescent element that emits light to the substrate 152 side by voltage application between the pixel electrode 191 and the common electrode 115 (see the light 321G and the light 321B).

The buffer layer 192, the light-emitting layer 193, and the buffer layer 194 can also be referred to as organic layers (layers containing an organic compound) or EL layers. The pixel electrode 191 preferably has a function of reflecting visible light. The common electrode 115 has a function of transmitting visible light.

The pixel electrode 191 is electrically connected to a source or a drain of the transistor 342 through an opening provided in the insulating layer 214. The transistor 342 has a function of controlling the driving of the light-emitting element or the light-emitting and light-receiving element.

At least part of a circuit electrically connected to the light-emitting and light-receiving element 190MER is preferably formed using the same material in the same steps as a circuit electrically connected to the light-emitting element 190G and the light-emitting element 190B. In that case, the thickness of the display device can be reduced compared with the case where the two circuits are separately formed, resulting in simplification of the manufacturing process.

The light-emitting and light-receiving element 190MER, the light-emitting element 190G, and the light-emitting element 190B are preferably covered with a protective layer 195. In FIG. 21A and the like, the protective layer 195 is provided over and in contact with the common electrode 115. Providing the protective layer 195 can inhibit entry of impurities into the light-emitting and light-receiving element 190MER and the light-emitting elements of different colors and improve the light-emitting and light-receiving element 190MER and the light-emitting devices of the different colors. The protective layer 195 and the substrate 152 are bonded to each other with an adhesive layer 142.

A light-blocking layer BM is provided on a surface of the substrate 152 that faces the substrate 151. The light-blocking layer BM has openings at positions overlapping the light-emitting element 190G and the light-emitting element 190B and a position overlapping the light-emitting and light-receiving element 190MER. Note that in this specification and the like, the position overlapping the light-emitting element 190G or the light-emitting element 190B refers specifically to a position overlapping a light-emitting region of the light-emitting element 190G or the light-emitting element 190B. Similarly, the position overlapping the light-emitting and light-receiving element 190MER refers specifically to a position overlapping a light-emitting region and a light-receiving region of the light-emitting and light-receiving element 190MER.

As illustrated in FIG. 21B, the light-emitting and light-receiving element 190MER is capable of detecting light that is emitted from the light-emitting element 190G or the light-emitting element 190B and then reflected by an object. However, in some cases, light emitted from the light-emitting element 190G or the light-emitting element 190B is reflected inside the display device 310A and enters the light-emitting and light-receiving element 190MER without involving an object. The light-blocking layer BM can reduce the influence of such stray light. For example, in the case where the light-blocking layer BM is not provided, light 323 emitted from the light-emitting element 190G is reflected by the substrate 152 and reflected light 324 enters the light-emitting and light-receiving element 190MER in some cases. Providing the light-blocking layer BM can inhibit the reflected light 324 from entering the light-emitting and light-receiving element 190MER. Consequently, noise can be reduced, and the sensitivity of a sensor using the light-emitting and light-receiving element 190MER can be increased.

For the light-blocking layer BM, a material that blocks light emitted from the light-emitting elements can be used. The light-blocking layer BM preferably absorbs visible light. As the light-blocking layer BM, a black matrix can be formed using a metal material or a resin material containing pigment (e.g., carbon black) or dye, for example. The light-blocking layer BM may have a stacked-layer structure of a red color filter, a green color filter, and a blue color filter.

[Display Device 310B]

A display device 310B illustrated in FIG. 22A is different from the display device 310A in that each of the light-emitting element 190G, the light-emitting element 190B, and the light-emitting and light-receiving element 190MER does not include the buffer layer 192 and the buffer layer 194 and includes the common layer 112 and the common layer 114. Note that in the following description of the display device, components similar to those of the above-mentioned display device are not described in some cases.

Note that the layered structure of the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER is not limited to the structures in the display devices 310A and 310B. For example, any of the layered structures illustrated in FIG. 17 to FIG. 20 can be appropriately used for each element.

[Display Device 310C]

A display device 310C illustrated in FIG. 22B is different from the display device 310B in that the substrate 151 and the substrate 152 are not included but a substrate 153, a substrate 154, an adhesive layer 155, and an insulating layer 212 are included.

The substrate 153 and the insulating layer 212 are bonded to each other with the adhesive layer 155. The substrate 154 and the protective layer 195 are bonded to each other with the adhesive layer 142.

The display device 310C has a structure obtained in such a manner that the insulating layer 212, the transistor 342, the light-emitting and light-receiving element 190MER, the light-emitting element 190G, the light-emitting element 190B, and the like are formed over a formation substrate and then transferred onto the substrate 153. The substrate 153 and the substrate 154 preferably have flexibility. Accordingly, the flexibility of the display device 310C can be increased. For example, a resin is preferably used for the substrate 153 and the substrate 154.

For the substrate 153 and the substrate 154, it is possible to use, for example, a polyester resin such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), a polyacrylonitrile resin, an acrylic resin, a polyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC) resin, a polyether sulfone (PES) resin, a polyamide resin (e.g., nylon or aramid), a polysiloxane resin, a cycloolefin resin, a polystyrene resin, a polyamide-imide resin, a polyurethane resin, a polyvinyl chloride resin, a polyvinylidene chloride resin, a polypropylene resin, a polytetrafluoroethylene (PTFE) resin, an ABS resin, or cellulose nanofiber. Glass that is thin enough to have flexibility may be used for one or both of the substrate 153 and the substrate 154.

As the substrate included in the display device of this embodiment, a film having high optical isotropy may be used. Examples of the film having high optical isotropy include a triacetyl cellulose (TAC, also referred to as cellulose triacetate) film, a cycloolefin polymer (COP) film, a cycloolefin copolymer (COC) film, and an acrylic film.

A more detailed structure of the display device of one embodiment of the present invention will be described below with reference to FIG. 23 to FIG. 26 .

[Display Device 100A]

FIG. 23 is a perspective view of a display device 100A, and FIG. 24 is a cross-sectional view of the display device 100A.

The display device 100A has a structure in which the substrate 152 and the substrate 151 are bonded to each other. In FIG. 23 , the substrate 152 is denoted by a dashed line.

The display device 100A includes a display portion 162, a circuit 164, a wiring 165, and the like. FIG. 23 illustrates an example in which the display device 100A is provided with an IC (integrated circuit) 173 and an FPC 172. Thus, the structure illustrated in FIG. 23 can be regarded as a display module including the display device 100A, the IC, and the FPC.

As the circuit 164, for example, a scan line driver circuit can be used.

The wiring 165 has a function of supplying a signal and power to the display portion 162 and the circuit 164. The signal and power are input to the wiring 165 from the outside through the FPC 172 or from the IC 173.

FIG. 23 illustrates an example in which the IC 173 is provided over the substrate 151 by a COG (Chip On Glass) method, a COF (Chip on Film) method, or the like. An IC including a scan line driver circuit or a signal line driver circuit, for example, can be used as the IC 173. Note that the display device 100A and the display module may have a structure not including an IC. The IC may be mounted on the FPC by a COF method or the like.

FIG. 24 illustrates an example of cross sections of part of a region including the FPC 172, part of a region including the circuit 164, part of a region including the display portion 162, and part of a region including an end portion of the display device 100A illustrated in FIG. 23 .

The display device 100A in FIG. 24 includes a transistor 201, a transistor 205, a transistor 206, a transistor 207, the light-emitting element 190B, the light-emitting element 190G, the light-emitting and light-receiving element 190MER, and the like between the substrate 151 and the substrate 152.

The substrate 152 and the insulating layer 214 are attached to each other with the adhesive layer 142. A solid sealing structure, a hollow sealing structure, or the like can be employed to seal the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER. In FIG. 24 , a hollow sealing structure is employed in which a space 143 surrounded by the substrate 152, the adhesive layer 142, and the insulating layer 214 is filled with an inert gas (e.g., nitrogen or argon). The adhesive layer 142 may be provided to overlap the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER. The space 143 surrounded by the substrate 152, the adhesive layer 142, and the insulating layer 214 may be filled with a resin different from that of the adhesive layer 142.

The light-emitting element 190B has a layered structure in which the pixel electrode 191, the common layer 112, the light-emitting layer 193B, the common layer 114, and the common electrode 115 are stacked in this order from the insulating layer 214 side. The pixel electrode 191 is connected to a conductive layer 222 b included in the transistor 207 through an opening provided in the insulating layer 214. The transistor 207 has a function of controlling the driving of the light-emitting element 190B. The end portion of the pixel electrode 191 is covered with the partition 216. The pixel electrode 191 contains a material that reflects visible light, and the common electrode 115 contains a material that transmits visible light.

The light-emitting element 190G has a layered structure in which the pixel electrode 191, the common layer 112, the light-emitting layer 193G, the common layer 114, and the common electrode 115 are stacked in this order from the insulating layer 214 side. The pixel electrode 191 is connected to the conductive layer 222 b included in the transistor 206 through an opening provided in the insulating layer 214. The transistor 206 has a function of controlling the driving of the light-emitting element 190G.

The light-emitting and light-receiving element 190MER has a layered structure in which the pixel electrode 191, the common layer 112, the active layer 183, the light-emitting layer 193R, the common layer 114, and the common electrode 115 are stacked in this order from the insulating layer 214 side. The pixel electrode 191 is electrically connected to the conductive layer 222 b included in the transistor 205 through an opening provided in the insulating layer 214. The transistor 205 has a function of controlling the driving of the light-emitting and light-receiving element 190MER.

Light emitted from the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER is emitted toward the substrate 152. Light enters the light-emitting and light-receiving element 190MER through the substrate 152 and the space 143. For the substrate 152, a material that has high transmittance with respect to visible light is preferably used.

The pixel electrodes 191 can be formed using the same material in the same step. The common layer 112, the common layer 114, and the common electrode 115 are used in common in the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER. The light-emitting and light-receiving element 190MER has the structure of a red-light-emitting element to which the active layer 183 is added. Alternatively, the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER can have a common structure except for the active layer 183 and the light-emitting layer 193 of each color. Thus, the display portion 162 of the display device 100A can have a light-receiving function without a significant increase in the number of manufacturing steps.

The light-blocking layer BM is provided on a surface of the substrate 152 that faces the substrate 151. The light-blocking layer BM includes openings at positions overlapping the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER. Providing the light-blocking layer BM can control the range where the light-emitting and light-receiving element 190MER detects light. Furthermore, with the light-blocking layer BM, light can be prevented from directly entering the light-emitting and light-receiving element 190MER from the light-emitting element 190G or the light-emitting element 190B without involving any object. Hence, a sensor with less noise and high sensitivity can be obtained.

The transistor 201, the transistor 205, the transistor 206, and the transistor 207 are formed over the substrate 151. These transistors can be formed using the same materials in the same steps.

An insulating layer 211, an insulating layer 213, an insulating layer 215, and the insulating layer 214 are provided in this order over the substrate 151. Parts of the insulating layer 211 function as gate insulating layers of the transistors. Parts of the insulating layer 213 function as gate insulating layers of the transistors. The insulating layer 215 is provided to cover the transistors. The insulating layer 214 is provided to cover the transistors and has a function of a planarization layer. Note that there is no limitation on the number of gate insulating layers and the number of insulating layers covering the transistors, and each insulating layer may be either a single layer or two or more layers.

A material into which impurities such as water or hydrogen do not easily diffuse is preferably used for at least one of the insulating layers that cover the transistors. This allows the insulating layer to serve as a barrier layer. Such a structure can effectively inhibit diffusion of impurities into the transistors from the outside and increase the reliability of the display device.

An inorganic insulating film is preferably used as each of the insulating layer 211, the insulating layer 213, and the insulating layer 215. As the inorganic insulating film, for example, a silicon nitride film, a silicon oxynitride film, a silicon oxide film, a silicon nitride oxide film, an aluminum oxide film, an aluminum nitride film, or the like can be used. A hafnium oxide film, a hafnium oxynitride film, a hafnium nitride oxide film, an yttrium oxide film, a zirconium oxide film, a gallium oxide film, a tantalum oxide film, a magnesium oxide film, a lanthanum oxide film, a cerium oxide film, a neodymium oxide film, or the like may be used. A stack including two or more of the above insulating films may also be used. Note that a base film may be provided between the substrate 151 and the transistors. Any of the above-described inorganic insulating films can be used as the base film.

Here, an organic insulating film often has a lower barrier property than an inorganic insulating film. Therefore, the organic insulating film preferably has an opening in the vicinity of an end portion of the display device 100A. This can inhibit entry of impurities from the end portion of the display device 100A through the organic insulating film. Alternatively, the organic insulating film may be formed so that an end portion of the organic insulating film is positioned on the inner side compared to the end portion of the display device 100A, to prevent the organic insulating film from being exposed at the end portion of the display device 100A.

An organic insulating film is suitable for the insulating layer 214 functioning as a planarization layer. Examples of materials that can be used for the organic insulating film include an acrylic resin, a polyimide resin, an epoxy resin, a polyamide resin, a polyimide-amide resin, a siloxane resin, a benzocyclobutene-based resin, a phenol resin, and precursors of these resins.

In a region 228 illustrated in FIG. 24 , an opening is formed in the insulating layer 214. This can inhibit entry of impurities into the display portion 162 from the outside through the insulating layer 214 even when an organic insulating film is used as the insulating layer 214. Thus, the reliability of the display device 100A can be increased.

The transistor 201, the transistor 205, the transistor 206, and the transistor 207 each include a conductive layer 221 functioning as a gate, the insulating layer 211 functioning as a gate insulating layer, a conductive layer 222 a and the conductive layer 222 b functioning as a source and a drain, a semiconductor layer 231, the insulating layer 213 functioning as a gate insulating layer, and a conductive layer 223 functioning as a gate. Here, a plurality of layers obtained by processing the same conductive film are shown with the same hatching pattern. The insulating layer 211 is positioned between the conductive layer 221 and the semiconductor layer 231. The insulating layer 213 is positioned between the conductive layer 223 and the semiconductor layer 231.

There is no particular limitation on the structure of the transistors included in the display device of this embodiment. For example, a planar transistor, a staggered transistor, or an inverted staggered transistor can be used. A top-gate or a bottom-gate transistor structure may be employed. Alternatively, gates may be provided above and below a semiconductor layer in which a channel is formed.

The structure in which the semiconductor layer where a channel is formed is provided between two gates is used for the transistor 201, the transistor 205, the transistor 206, and the transistor 207. The two gates may be connected to each other and supplied with the same signal to drive the transistor. Alternatively, a potential for controlling the threshold voltage may be supplied to one of the two gates and a potential for driving may be supplied to the other to control the threshold voltage of the transistor.

There is no particular limitation on the crystallinity of a semiconductor material used in the transistor, and any of an amorphous semiconductor or a semiconductor having crystallinity (a microcrystalline semiconductor, a polycrystalline semiconductor, a single crystal semiconductor, or a semiconductor partly including crystal regions) may be used. A semiconductor having crystallinity is preferably used, in which case deterioration of the transistor characteristics can be inhibited.

A semiconductor layer of a transistor preferably includes a metal oxide (also referred to as an oxide semiconductor). Alternatively, the semiconductor layer of the transistor may include silicon. Examples of silicon include amorphous silicon and crystalline silicon (e.g., low-temperature polysilicon and single crystal silicon).

The semiconductor layer preferably includes indium, M (M is one or more kinds selected from gallium, aluminum, silicon, boron, yttrium, tin, copper, vanadium, beryllium, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium), and zinc, for example. In particular, M is preferably one or more kinds selected from aluminum, gallium, yttrium, and tin.

It is particularly preferable to use an oxide containing indium (In), gallium (Ga), and zinc (Zn) (also referred to as IGZO) for the semiconductor layer. Alternatively, it is preferable to use an oxide containing indium, gallium, zinc, and tin. Alternatively, it is preferable to use an oxide containing indium and zinc.

When the semiconductor layer is an In-M-Zn oxide, the atomic ratio of In is preferably greater than or equal to the atomic ratio of M in the In-M-Zn oxide. Examples of the atomic ratio of the metal elements in such an In-M-Zn oxide include In:M:Zn=1:1:1 or a composition in the neighborhood thereof, In:M:Zn=1:1:1.2 or a composition in the neighborhood thereof, In:M:Zn=2:1:3 or a composition in the neighborhood thereof, In:M:Zn=3:1:2 or a composition in the neighborhood thereof, In:M:Zn=4:2:3 or a composition in the neighborhood thereof, In:M:Zn=4:2:4.1 or a composition in the neighborhood thereof, In:M:Zn=5:1:3 or a composition in the neighborhood thereof, In:M:Zn=5:1:6 or a composition in the neighborhood thereof, In:M:Zn=5:1:7 or a composition in the neighborhood thereof, In:M:Zn=5:1:8 or a composition in the neighborhood thereof, In:M:Zn=10:1:3 or a composition in the neighborhood thereof, In:M:Zn=6:1:6 or a composition in the neighborhood thereof, and In:M:Zn=5:2:5 or a composition in the neighborhood thereof. Note that a composition in the neighborhood includes the range of ±30% of an intended atomic ratio.

For example, when the atomic ratio is described as In:Ga:Zn=4:2:3 or a composition in the neighborhood thereof, the case is included where the atomic ratio of Ga is greater than or equal to 1 and less than or equal to 3 and the atomic ratio of Zn is greater than or equal to 2 and less than or equal to 4 with the atomic ratio of In being 4. When the atomic ratio is described as In:Ga:Zn=5:1:6 or a composition in the neighborhood thereof, the case is included where the atomic ratio of Ga is greater than 0.1 and less than or equal to 2 and the atomic ratio of Zn is greater than or equal to 5 and less than or equal to 7 with the atomic ratio of In being 5. When the atomic ratio is described as In:Ga:Zn=1:1:1 or a composition in the neighborhood thereof, the case is included where the atomic ratio of Ga is greater than 0.1 and less than or equal to 2 and the atomic ratio of Zn is greater than 0.1 and less than or equal to 2 with the atomic ratio of In being 1.

The transistor included in the circuit 164 and the transistor included in the display portion 162 may have the same structure or different structures. A plurality of transistors included in the circuit 164 may have the same structure or two or more kinds of structures. Similarly, a plurality of transistors included in the display portion 162 may have the same structure or two or more kinds of structures.

A connection portion 204 is provided in a region of the substrate 151 that is not overlapped by the substrate 152. In the connection portion 204, the wiring 165 is electrically connected to the FPC 172 through a conductive layer 166 and a connection layer 242. On the top surface of the connection portion 204, the conductive layer 166 obtained by processing the same conductive film as the pixel electrode 191 is exposed. Thus, the connection portion 204 and the FPC 172 can be electrically connected to each other through the connection layer 242.

A variety of optical members can be arranged on the outer surface of the substrate 152. Examples of the optical members include a polarizing plate, a retardation plate, a light diffusion layer (e.g., a diffusion film), an anti-reflective layer, and a light-condensing film. Furthermore, an antistatic film inhibiting the attachment of dust, a water repellent film inhibiting the attachment of stain, a hard coat film inhibiting generation of a scratch caused by the use, a shock absorbing layer, or the like may be provided on the outside of the substrate 152.

For each of the substrate 151 and the substrate 152, glass, quartz, ceramic, sapphire, a resin, or the like can be used. When a flexible material is used for the substrate 151 and the substrate 152, the flexibility of the display device can be increased.

As the adhesive layer, a variety of curable adhesives, e.g., a photocurable adhesive such as an ultraviolet curable adhesive, a reactive curable adhesive, a thermosetting adhesive, and an anaerobic adhesive can be used. Examples of these adhesives include an epoxy resin, an acrylic resin, a silicone resin, a phenol resin, a polyimide resin, an imide resin, a PVC (polyvinyl chloride) resin, a PVB (polyvinyl butyral) resin, and an EVA (ethylene vinyl acetate) resin. In particular, a material with low moisture permeability, such as an epoxy resin, is preferred. Alternatively, a two-component resin may be used. An adhesive sheet or the like may be used.

As the connection layer, an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), or the like can be used.

Examples of materials that can be used for a gate, a source, and a drain of a transistor and conductive layers such as a variety of wirings and electrodes included in a display device include metals such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, or tungsten, and an alloy containing any of these metals as its main component. A film containing any of these materials can be used as a single layer or in a stacked-layer structure.

As a light-transmitting conductive material, a conductive oxide such as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zinc oxide containing gallium, or graphene can be used. Alternatively, a metal material such as gold, silver, platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, or titanium, or an alloy material containing the metal material can be used. Further alternatively, a nitride of the metal material (e.g., titanium nitride) or the like may be used. Note that in the case of using the metal material or the alloy material (or the nitride thereof), the thickness is preferably set small enough to be able to transmit light. A stacked film of any of the above materials can be used as a conductive layer. For example, a stacked film of indium tin oxide and an alloy of silver and magnesium is preferably used, in which case the conductivity can be increased. These materials can also be used for conductive layers such as a variety of wirings and electrodes included in a display device, or conductive layers (conductive layers functioning as a pixel electrode, a common electrode, or the like) included in a light-emitting element and a light-emitting and light-receiving element.

Examples of an insulating material that can be used for each insulating layer include a resin such as an acrylic resin and an epoxy resin, and an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, and aluminum oxide.

[Display Device 100B]

FIG. 25 is a cross-sectional view of a display device 100B.

The display device 100B is different from the display device 100A mainly in including the protective layer 195. Detailed description of a structure similar to that of the display device 100A is omitted.

Providing the protective layer 195 that covers the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER can inhibit entry of impurities such as water into the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER, leading to an increase in the reliability of the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER.

In the region 228 in the vicinity of an end portion of the display device 100B, the insulating layer 215 and the protective layer 195 are preferably in contact with each other through an opening in the insulating layer 214. In particular, the inorganic insulating film included in the insulating layer 215 and the inorganic insulating film included in the protective layer 195 are preferably in contact with each other. Thus, entry of impurities from the outside into the display portion 162 through the organic insulating film can be inhibited. Consequently, the reliability of the display device 100B can be increased.

The protective layer 195 may have a single-layer structure or a stacked-layer structure; for example, the protective layer 195 may have a three-layer structure that includes an inorganic insulating layer over the common electrode 115, an organic insulating layer over the inorganic insulating layer, and an inorganic insulating layer over the organic insulating layer. In that case, an end portion of the inorganic insulating film preferably extends beyond an end portion of the organic insulating film.

Furthermore, a lens may be provided in a region overlapping the light-emitting and light-receiving element 190MER. Thus, the sensitivity and accuracy of a sensor using the light-emitting and light-receiving element 190MER can be increased.

The lens preferably has a refractive index greater than or equal to 1.3 and less than or equal to 2.5. The lens can be formed using at least one of an inorganic material and an organic material. For example, a material containing a resin can be used for the lens. Moreover, a material containing at least one of an oxide and a sulfide can be used for the lens.

Specifically, a resin containing chlorine, bromine, or iodine, a resin containing a heavy metal atom, a resin having an aromatic ring, a resin containing sulfur, and the like can be used for the lens. Alternatively, a material containing a resin and nanoparticles of a material having a higher refractive index than the resin can be used for the lens. Titanium oxide, zirconium oxide, or the like can be used for the nanoparticles.

In addition, cerium oxide, hafnium oxide, lanthanum oxide, magnesium oxide, niobium oxide, tantalum oxide, titanium oxide, yttrium oxide, zinc oxide, an oxide containing indium and tin, an oxide containing indium, gallium, and zinc, and the like can be used for the lens. Alternatively, zinc sulfide and the like can be used for the lens.

In the display device 100B, the protective layer 195 and the substrate 152 are bonded to each other with the adhesive layer 142. The adhesive layer 142 is provided to overlap the light-emitting element 190B, the light-emitting element 190G, and the light-emitting and light-receiving element 190MER; that is, the display device 100B employs a solid sealing structure.

[Display Device 100C]

FIG. 26A is a cross-sectional view of a display device 100C.

The display device 100C is different from the display device 100B in transistor structures.

The display device 100C includes a transistor 208, a transistor 209, and a transistor 210 over the substrate 151.

The transistor 208, the transistor 209, and the transistor 210 each include the conductive layer 221 functioning as a gate, the insulating layer 211 functioning as a gate insulating layer, a semiconductor layer including a channel formation region 231 i and a pair of low-resistance regions 231 n, the conductive layer 222 a connected to one of the pair of low-resistance regions 231 n, the conductive layer 222 b connected to the other of the pair of low-resistance regions 231 n, an insulating layer 225 functioning as a gate insulating layer, the conductive layer 223 functioning as a gate, and the insulating layer 215 covering the conductive layer 223. The insulating layer 211 is positioned between the conductive layer 221 and the channel formation region 231 i. The insulating layer 225 is positioned between the conductive layer 223 and the channel formation region 231 i.

The conductive layer 222 a and the conductive layer 222 b are connected to the corresponding low-resistance regions 231 n through openings provided in the insulating layer 225 and the insulating layer 215. One of the conductive layer 222 a and the conductive layer 222 b serves as a source, and the other serves as a drain.

The pixel electrode 191 of the light-emitting element 190G is electrically connected to one of the pair of low-resistance regions 231 n of the transistor 208 through the conductive layer 222 b.

The pixel electrode 191 of the light-emitting and light-receiving element 190MER is electrically connected to the other of the pair of low-resistance regions 231 n of the transistor 209 through the conductive layer 222 b.

FIG. 26A illustrates an example in which the insulating layer 225 covers the top surface and a side surface of the semiconductor layer. Meanwhile, in a transistor 202 illustrated in FIG. 26B, the insulating layer 225 overlaps the channel formation region 231 i of the semiconductor layer 231 and does not overlap the low-resistance regions 231 n. The structure illustrated in FIG. 26B can be obtained by processing the insulating layer 225 using the conductive layer 223 as a mask, for example. In FIG. 26B, the insulating layer 215 is provided to cover the insulating layer 225 and the conductive layer 223, and the conductive layer 222 a and the conductive layer 222 b are connected to the low-resistance regions 231 n through openings in the insulating layer 215. Furthermore, an insulating layer 218 covering the transistor may be provided.

In addition, the display device 100C is different from the display device 100B in that neither the substrate 151 nor the substrate 152 is included and the substrate 153, the substrate 154, the adhesive layer 155, and the insulating layer 212 are included.

The substrate 153 and the insulating layer 212 are bonded to each other with the adhesive layer 155. The substrate 154 and the protective layer 195 are bonded to each other with the adhesive layer 142.

The display device 100C is formed in such a manner that the insulating layer 212, the transistor 208, the transistor 209, the transistor 210, the light-emitting and light-receiving element 190MER, the light-emitting element 190G, and the like which are formed over a formation substrate are transferred onto the substrate 153. The substrate 153 and the substrate 154 preferably have flexibility. Accordingly, the flexibility of the display device 100C can be increased.

The inorganic insulating film that can be used as the insulating layer 211, the insulating layer 213, and the insulating layer 215 can be used as the insulating layer 212.

In the display device of this embodiment, a subpixel exhibiting light of any of the colors includes a light-emitting and light-receiving element instead of a light-emitting element as described above. The light-emitting and light-receiving element functions as both a light-emitting element and a light-receiving element, whereby the pixel can have a light-receiving function without an increase in the number of subpixels included in the pixel. Moreover, the pixel can have a light-receiving function without a reduction in the resolution of the display device or the aperture ratio of each subpixel.

At least part of the structure examples, the drawings corresponding thereto, and the like exemplified in this embodiment can be implemented in combination with the other structure examples, the other drawings, and the like as appropriate.

Embodiment 4

[Structure Example of Display Device]

FIG. 27A is a block diagram of the display device 10. The display device 10 includes the display portion 11, the driver circuit 12A, the driver circuit 13, the driver circuit 14, the circuit 15, and the like.

The display portion 11 includes the plurality of pixels 30 arranged in a matrix. The pixels 30 each include a subpixel 21R, a subpixel 21G, a subpixel 21B, and an imaging pixel 22P. The subpixel 21R, the subpixel 21G, and the subpixel 21B each include a light-emitting element functioning as a display element. The imaging pixel 22P includes a light-receiving element functioning as a photoelectric conversion element.

The pixel 30 is electrically connected to the wiring GL, a wiring SLR, a wiring SLG, a wiring SLB, the wiring TX, the wiring SE, the wiring RS, the wiring WX, and the like. The wiring SLR, the wiring SLG, and the wiring SLB are electrically connected to the driver circuit 12A. The wiring GL is electrically connected to the driver circuit 13. The driver circuit 12A functions as a source line driver circuit (also referred to as a source driver). The driver circuit 13 functions as a gate line driver circuit (also referred to as a gate driver).

The pixels 30 each include the subpixel 21R, the subpixel 21G, and the subpixel 21B. For example, the subpixel 21R exhibits a red color, the subpixel 21G exhibits a green color, and the subpixel 21B exhibits a blue color. Thus, the display device 10 can perform full-color display. Note that although the example where the pixels 30 each include subpixels of three colors is shown here, subpixels of four or more colors may be included.

The subpixel 21R includes a light-emitting element emitting red light. The subpixel 21G includes a light-emitting element emitting green light. The subpixel 21B includes a light-emitting element emitting blue light. Note that the pixel 30 may include a subpixel including a light-emitting element emitting light of another color. For example, the pixel 30 may include, in addition to the three subpixels, a subpixel including a light-emitting element emitting white light, a subpixel including a light-emitting element emitting yellow light, or the like.

The wiring GL is electrically connected to the subpixel 21R, the subpixel 21G, and the subpixel 21B arranged in a row direction (an extending direction of the wiring GL). The wiring SLR, the wiring SLG, and the wiring SLB are electrically connected to the subpixels 21R, the subpixels 21G, and the subpixels 21B arranged in a column direction (an extending direction of the wiring SLR and the like), respectively.

The imaging pixel 22P included in the pixel 30 is electrically connected to the wiring TX, the wiring SE, the wiring RS, and the wiring WX. The wiring TX, the wiring SE, and the wiring RS are electrically connected to the driver circuit 14, and the wiring WX is electrically connected to the circuit 15.

The driver circuit 14 has a function of generating a signal for driving the imaging pixel 22P and outputting the signal to the imaging pixel 22P through the wiring SE, the wiring TX, and the wiring RS. The circuit 15 has a function of receiving a signal output from the imaging pixel 22P through the wiring WX and outputting the signal to the outside as image data. The circuit 15 functions as a reading circuit.

[Structure Example 1 of Pixel Circuit]

FIG. 27B illustrates an example of a circuit diagram of a pixel 21 that can be used as the subpixel 21R, the subpixel 21G, and the subpixel 21B. The pixel 21 includes the transistor M1, the transistor M2, the transistor M3, the capacitor C1, and a light-emitting element EL. The wiring GL and the wiring SL are electrically connected to the pixel 21. The wiring SL corresponds to any of the wiring SLR, the wiring SLG, and the wiring SLB illustrated in FIG. 27A.

A gate of the transistor M1 is electrically connected to the wiring GL, one of a source and a drain of the transistor M1 is electrically connected to the wiring SL, and the other thereof is electrically connected to one electrode of the capacitor C1 and a gate of the transistor M2. One of a source and a drain of the transistor M2 is electrically connected to the wiring AL, and the other of the source and the drain of the transistor M2 is electrically connected to one electrode of the light-emitting element EL, the other electrode of the capacitor C1, and one of a source and a drain of the transistor M3. A gate of the transistor M3 is electrically connected to the wiring GL, and the other of the source and the drain of the transistor M3 is electrically connected to the wiring RL. The other electrode of the light-emitting element EL is electrically connected to the wiring CL.

The transistor M1 and the transistor M3 each function as a switch. For example, the transistor M2 functions as a transistor that controls a current flowing through the light-emitting element EL.

Here, it is preferable to use LTPS transistors as all of the transistor M1 to the transistor M3. Alternatively, it is preferable to use OS transistors as the transistor M1 and the transistor M3 and to use an LTPS transistor as the transistor M2.

As the OS transistor, a transistor including an oxide semiconductor in a semiconductor layer in which a channel is formed can be used. The semiconductor layer preferably includes indium, M (M is one or more kinds selected from gallium, aluminum, silicon, boron, yttrium, tin, copper, vanadium, beryllium, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium), and zinc, for example. In particular, M is preferably one or more kinds selected from aluminum, gallium, yttrium, and tin. It is particularly preferable to use an oxide containing indium (In), gallium (Ga), and zinc (Zn) (also referred to as IGZO) for the semiconductor layer of the OS transistor. Alternatively, it is preferable to use an oxide containing indium (In), tin (Sn), and zinc (Zn). Further alternatively, it is preferable to use an oxide containing indium (In), gallium (Ga), tin (Sn), and zinc (Zn).

A transistor using an oxide semiconductor having a wider band gap and a lower carrier density than silicon can achieve an extremely low off-state current. Thus, such a low off-state current enables retention of electric charge accumulated in a capacitor that is connected in series with the transistor for along time. Therefore, it is particularly preferable to use a transistor using an oxide semiconductor as the transistor M1 and the transistor M3 each of which is connected in series with the capacitor C1. The use of the transistor containing an oxide semiconductor as each of the transistor M1 and the transistor M3 can prevent leakage of electric charge held in the capacitor C1 through the transistor M1 or the transistor M3. Furthermore, since electric charge held in the capacitor C1 can be held for a long time, a still image can be displayed for a long time without rewriting data in the pixel 21.

A data potential D is supplied to the wiring SL. A selection signal is supplied to the wiring GL. The selection signal includes a potential for turning on a transistor and a potential for turning off the transistor.

A reset potential is supplied to the wiring RL. An anode potential is supplied to the wiring AL. A cathode potential is supplied to the wiring CL. In the pixel 21, the anode potential is higher than the cathode potential. The reset potential supplied to the wiring RL can be set such that a potential difference between the reset potential and the cathode potential is lower than the threshold voltage of the light-emitting element EL. The reset potential can be a potential higher than the cathode potential, a potential equal to the cathode potential, or a potential lower than the cathode potential.

An example of a driving method of the case where the structure of the pixel 21 is applied to each of the subpixel 21R, the subpixel 21G, and the subpixel 21B illustrated in FIG. 27A is described with reference to a timing chart in FIG. 28A. FIG. 28A shows examples of signals input to the wiring GL, the wiring SLR, the wiring SLG, and the wiring SLB.

<Before Time T11>

Before Time T11, the subpixel 21R, the subpixel 21G, and the subpixel 21B are in the non-selected state. Before time T11, a potential for turning off the transistor M1 and the transistor M3 (here, a low-level potential) is supplied to the wiring GL.

<Period T11-T12>

A period from Time T11 to Time T12 corresponds to a period in which data is written to a pixel. At Time T11, a potential for turning on the transistor M1 and the transistor M3 (here, a high-level potential) is supplied to the wiring GL, and a first data potential DR, a first data potential DG, and a first data potential DB are supplied to the wiring SLR, the wiring SLG, and the wiring SLB, respectively. At this time, the transistor M1 is turned on, and the data potential is supplied to the gate of the transistor M2 from the wiring SLR, the wiring SLG, or the wiring SLB. In addition, the transistor M3 is turned on, and the reset potential is supplied to the one electrode of the light-emitting element EL from the wiring RL. Thus, light emission from the light-emitting element EL can be prevented during the writing period.

<After Time T12>

A period after Time T12 corresponds to a period in which data is written to the next row. At Time T12, a potential for turning off the transistor M1 and the transistor M3 is supplied to the wiring GL, and the transistor M1 and the transistor M3 are turned off. Thus, current corresponding to the gate potential of the transistor M2 flows through the light-emitting element EL, so that the light-emitting element EL emits light with desired luminance.

The above is the description of an example of the method for driving the pixel 21.

Structure Example 2 of Pixel Circuit

FIG. 27C illustrates an example of a circuit diagram of the imaging pixel 22P. The imaging pixel 22P includes a transistor M5, a transistor M6, a transistor M7, a transistor M8, the capacitor C2, a light-receiving element PD, and the like.

A gate of the transistor M5 is electrically connected to the wiring TX, one of a source and a drain of the transistor M5 is electrically connected to an anode electrode of the light-receiving element PD, and the other of the source and the drain of the transistor M5 is electrically connected to one of a source and a drain of the transistor M6, a first electrode of the capacitor C2, and agate of the transistor M7. A gate of the transistor M6 is electrically connected to the wiring RS, and the other of the source and the drain of the transistor M6 is electrically connected to a wiring Va. One of a source and a drain of the transistor M7 is electrically connected to a wiring Vc, and the other of the source and the drain of the transistor M7 is electrically connected to one of a source and a drain of the transistor M8. A gate of the transistor M8 is electrically connected to the wiring SE, and the other of the source and the drain of the transistor M8 is electrically connected to the wiring WX. A cathode electrode of the light-receiving element PD is electrically connected to the wiring CL. A second electrode of the capacitor C2 is electrically connected to a wiring Vb.

The transistor M5, the transistor M6, and the transistor M8 function as switches. The transistor M7 functions as an amplifier element (amplifier).

It is preferable to use LTPS transistors as all of the transistor M5 to the transistor M8. Alternatively, it is preferable to use OS transistors as the transistor M5 and the transistor M6 and to use an LTPS transistor as the transistor M7. At this time, the transistor M8 may be either an OS transistor or an LTPS transistor.

By using OS transistors as the transistor M5 and the transistor M6, a potential held in the gate of the transistor M7 on the basis of electric charge generated in the light-receiving element PD can be prevented from leaking through the transistor M5 or the transistor M6.

For example, in the case where image capturing is performed using a global shutter system, a period from the end of electric charge transfer operation to the start of reading operation (charge holding period) varies among pixels. For example, when an image having the same grayscale value in all the pixels is captured, output signals in all the pixels ideally have potentials of the same level. However, in the case where the length of the charge holding period varies row by row, if electric charge accumulated at nodes in the pixels in each row leaks out over time, the potential of an output signal in a pixel varies row by row, and image data varies in grayscale level row by row. Thus, when the OS transistors are used as the transistor M5 and the transistor M6, such a potential change at the node can be extremely small. That is, even when image capturing is performed using the global shutter system, it is possible to inhibit variation in grayscale of image data due to a difference in the length of the charge holding period, and it is possible to enhance the quality of captured images.

Meanwhile, it is preferable to use, as the transistor M7, an LTPS transistor using low-temperature polysilicon as a semiconductor layer. The LTPS transistor can have a higher field-effect mobility than the OS transistor, and has excellent drive capability and current capability. Thus, the transistor M7 can operate at higher speed than the transistor M5 and the transistor M6. By using the LTPS transistor as the transistor M7, an output in accordance with the extremely low potential based on the amount of light received by the light-receiving element PD can be quickly supplied to the transistor M8.

In other words, in the imaging pixel 22P, the transistor M5 and the transistor M6 have low leakage current and the transistor M7 has high drive capability, whereby, when the light-receiving element PD receives light, the electric charge transferred through the transistor M5 can be held without leakage and high-speed reading can be performed.

Low off-state current, high-speed operation, and the like, which are required for the transistor M5 to the transistor M7, are not necessarily required for the transistor M8, which functions as a switch for supplying the output from the transistor M7 to the wiring WX. For this reason, either low-temperature polysilicon or an oxide semiconductor may be used for the semiconductor layer of the transistor M8.

Note that although n-channel transistors are shown as the transistors in FIG. 27B and FIG. 27C, p-channel transistors can also be used.

The transistors included in the pixel 21 and the imaging pixel 22P are preferably arranged over the same substrate.

An example of a method for driving the imaging pixel 22P illustrated in FIG. 27C is described with reference to a timing chart in FIG. 28B. FIG. 28B shows signals input to the wiring TX, the wiring SE, the wiring RS, and the wiring WX.

<Before Time T21>

Before Time T21, a low-level potential is supplied to the wiring TX, the wiring SE, and the wiring RS. Data is not output to the wiring WX, and the wiring WX is regarded as being set to a low-level potential here. Note that a predetermined potential may be supplied to the wiring WX.

<Period T21-T22>

At Time T21, a potential for turning on a transistor (here, a high-level potential) is supplied to the wiring TX and the wiring RS. In addition, a potential for turning off a transistor (here, a low-level potential) is supplied to the wiring SE.

At this time, the transistor M5 and the transistor M6 are turned on, so that a potential lower than the potential of the cathode electrode of the light-receiving element PD is supplied to the anode electrode of the light-receiving element PD from the wiring Va through the transistor M6 and the transistor M5. That is, reverse bias voltage is applied to the light-receiving element PD.

In addition, the potential of the wiring Va is also supplied to the first electrode of the capacitor C2, so that charge is stored in the capacitor C2.

Period T21-T22 can also be referred to as a reset (initialization) period.

<Period T22-T23>

At Time T22, a low-level potential is supplied to the wiring TX and the wiring RS. Accordingly, the transistor M5 and the transistor M6 are each turned off.

The transistor M5 is turned off, so that the reverse bias voltage is retained in the light-receiving element PD. Here, photoelectric conversion is caused by light incident on the light-receiving element PD, and charge is accumulated in the anode electrode of the light-receiving element PD.

Period T22-T23 can also be referred to as an exposure period. The exposure period is set in accordance with the sensitivity of the light-receiving element PD, the amount of incident light, or the like and is preferably set to be much longer than at least the reset period.

In addition, in Period T22-T23, the transistor M5 and the transistor M6 are turned off, so that the potential of the first electrode of the capacitor C2 is held at a low-level potential supplied from the wiring Va.

<Period T23-T24>

At Time T23, a high-level potential is supplied to the wiring TX. Accordingly, the transistor M5 is turned on, and the charge accumulated in the light-receiving element PD is transferred to the first electrode of the capacitor C2 through the transistor M5. Accordingly, the potential of a node to which the first electrode of the capacitor C2 is connected increases in accordance with the amount of the charge accumulated in the light-receiving element PD. Consequently, a potential corresponding to the amount of light to which the light-receiving element PD is exposed is supplied to the gate of the transistor M7.

<Period T24-T25>

At Time T24, a low-level potential is supplied to the wiring TX. Thus, the transistor M5 is turned off, and a node to which the gate of the transistor M7 is connected is brought into a floating state. Since the light-receiving element PD is continuously exposed to light, a change in the potential of the node to which the gate of the transistor M7 is connected can be prevented by turning off the transistor M5 after the transfer operation in Period T23-T24 is completed.

<Period T25-T26>

At Time T25, a high-level potential is supplied to the wiring SE. Accordingly, the transistor M8 is turned on. Period T25-T26 can also be referred to as a reading period.

For example, a source follower circuit is formed using the transistor M7 and a transistor included in the circuit 15, so that data can be read. In this case, the data potential DS output to the wiring WX is determined in accordance with a gate potential of the transistor M7. Specifically, a potential obtained by subtracting the threshold voltage of the transistor M7 from the gate potential of the transistor M7 is output to the wiring WX as the data potential DS, and the potential is read by the reading circuit included in the circuit 15.

Note that a source ground circuit is composed of the transistor M7 and the transistor included in the circuit 15 so that data can be read by the reading circuit included in the circuit 15.

<At and after Time T26>

At Time T26, a low-level potential is supplied to the wiring SE. Accordingly, the transistor M8 is turned off. Accordingly, data reading in the imaging pixel 22P is completed. After Time T26, data reading operation is sequentially performed in the next rows.

When the driving method shown in FIG. 28B is used, the exposure period and the reading period can be set independently; therefore, light exposure can be concurrently performed on all the imaging pixels 22P in the display portion 11, and then data can be sequentially read. Accordingly, what is called global shutter driving can be achieved. In the case of performing global shutter driving, a transistor including an oxide semiconductor, which has an extremely low leakage current in an off-state, is preferably used as a transistor functioning as a switch in the imaging pixel 22P (in particular, each of the transistor M5 and the transistor M6).

The above is the description of the example of the method for driving the imaging pixel 22P.

[Modification Example of Pixel Circuit]

Structure examples of the pixel 21 and the imaging pixel 22P, which are different from the above, are described below.

Note that transistors each including a pair of gates overlapping with each other with a semiconductor layer therebetween can be used as the transistors included in the pixel 21 and the imaging pixel 22P. Specific examples of an LTPS transistor including a pair of gates and an OS transistor including a pair of gates are described in detail below.

In the transistor including a pair of gates, the same potential is supplied to the pair of gates electrically connected to each other, whereby on-state current of the transistor can be increased and the saturation characteristics can be improved. A potential for controlling the threshold voltage of the transistor may be supplied to one of the pair of gates. Furthermore, when a constant potential is supplied to one of the pair of gates, the stability of the electrical characteristics of the transistor can be improved. For example, one of the gates of the transistor may be electrically connected to a wiring to which a constant potential is supplied or may be electrically connected to a source or a drain of the transistor.

Structure Example 1 of Display Device

FIG. 29A illustrates a schematic view of a display device 50. The display device 50 includes a substrate 51, a substrate 52, a light-receiving element 53, a light-emitting element 57R, a light-emitting element 57G, a light-emitting element 57B, a functional layer 55, and the like.

The light-emitting element 57R, the light-emitting element 57G, the light-emitting element 57B, and the light-receiving element 53 are provided between the substrate 51 and the substrate 52.

The light-emitting element 57R, the light-emitting element 57G, and the light-emitting element 57B emit red (R) light, green (G) light, and blue (B) light, respectively.

The display device 50 includes a plurality of pixels arranged in a matrix. One pixel includes one or more subpixels. One subpixel includes one light-emitting element. For example, the pixel can have a structure including three subpixels (e.g., three colors of R, G, and B or three colors of yellow (Y), cyan (C), and magenta (M)) or four subpixels (e.g., four colors of R, G, B, and white (W) or four colors of R, G, B, and Y). The pixel further includes the light-receiving element 53. The light-receiving element 53 may be provided in all the pixels or may be provided in some of the pixels. In addition, one pixel may include a plurality of light-receiving elements 53.

FIG. 29A illustrates a finger 60 touching a surface of the substrate 52. Part of light emitted from the light-emitting element 57G is reflected or scattered at a contact portion of the substrate 52 and the finger 60. Then, part of the reflected light or scattered light enters the light-receiving element 53, and the contact of the finger 60 with the substrate 52 can be detected. That is, the display device 50 can function as a touch panel.

The functional layer 55 includes a circuit that drives the light-emitting element 57R, the light-emitting element 57G, and the light-emitting element 57B and a circuit that drives the light-receiving element 53. The functional layer 55 is provided with a switch, a transistor, a capacitor, a wiring, and the like. Note that in the case where the light-emitting element 57R, the light-emitting element 57G, the light-emitting element 57B, and the light-receiving element 53 are driven by a passive-matrix method, a structure not provided with a switch or a transistor may be employed.

The display device 50 may have a function of detecting a fingerprint of the finger 60. FIG. 29B schematically illustrates an enlarged view of the contact portion in a state where the finger 60 touches the substrate 52. FIG. 29B illustrates light-emitting elements 57 and the light-receiving elements 53 that are alternately arranged.

The fingerprint of the finger 60 is formed of depressions and projections. Therefore, as illustrated in FIG. 29B, the projections of the fingerprint touch the substrate 52, and scattered light (indicated by dashed arrows) occurs at the contact surfaces.

As illustrated in FIG. 29B, in the intensity distribution of the scattered light on the surface where the finger 60 touches the substrate 52, the intensity of light almost perpendicular to the contact surface is the highest, and the intensity of light becomes lower as an angle becomes larger in an oblique direction. Thus, the intensity of light received by the light-receiving element 53 positioned directly below the contact surface (i.e., overlapping with the contact surface) is the highest. Scattered light at greater than or equal to a predetermined scattering angle is fully reflected in the other surface (a surface opposite to the contact surface) of the substrate 52 and does not pass through the light-receiving element 53. As a result, a clear fingerprint image can be captured.

In the case where an arrangement interval between the light-receiving elements 53 is smaller than a distance between two projections of a fingerprint, preferably a distance between a depression and a projection adjacent to each other, a clear fingerprint image can be obtained. The distance between a depression and a projection of a human's fingerprint is approximately 200 μm; thus, the arrangement interval between the light-receiving elements 53 is, for example, less than or equal to 400 μm, preferably less than or equal to 200 μm, further preferably less than or equal to 150 μm, still further preferably less than or equal to 100 μm, even still further preferably less than or equal to 50 μm and greater than or equal to 1 μm, preferably greater than or equal to 10 μm, further preferably greater than or equal to 20 μm.

FIG. 29C illustrates an example of a fingerprint image captured with the display device 50. In an image-capturing range 63 in FIG. 29C, the outline of the finger 60 is indicated with a dashed line and the outline of a contact portion 61 is indicated with a dashed-dotted line. In the contact portion 61, a high-contrast image of a fingerprint 62 can be captured owing to a difference in the amount of light incident on the light-receiving elements 53.

The display device 50 can also function as a touch panel or a pen tablet. FIG. 29D illustrates a state in which a tip of a stylus 65 slides in a direction indicated by a dashed arrow while the tip of the stylus 65 touches the substrate 52.

As illustrated in FIG. 29D, when light scattered at the contact surface of the tip of the stylus 65 and the substrate 52 is incident on the light-receiving element 53 that overlaps with the contact surface, the position of the tip of the stylus 65 can be detected with high accuracy.

FIG. 29E illustrates an example of a path 66 of the stylus 65 that is detected by the display device 50. The display device 50 can detect the position of an object to be detected, such as the stylus 65, with high position accuracy, so that high-resolution drawing can be performed using a drawing application or the like. Unlike the case of using a capacitive touch sensor, an electromagnetic induction touch pen, or the like, the display device 50 can detect even the position of a highly insulating object to be detected, the material of a tip portion of the stylus 65 is not limited, and a variety of writing materials (e.g., a brush, a glass pen, a quill pen, and the like) can be used.

Here, FIG. 29F to FIG. 29H illustrate examples of a pixel that can be used in the display device 50.

Pixels illustrated in FIG. 29F and FIG. 29G include the light-emitting element 57R for red (R), the light-emitting element 57G for green (G), the light-emitting element 57B for blue (B), and the light-receiving element 53. The pixels each include a pixel circuit for driving the light-emitting element 57R, the light-emitting element 57G, the light-emitting element 57B, and the light-receiving element 53.

FIG. 29F illustrates an example in which three light-emitting elements and one light-receiving element are provided in a matrix of 2×2. FIG. 29G illustrates an example in which three light-emitting elements are laterally arranged in a line and one laterally long light-receiving element 53 is provided below the three light-emitting elements.

The pixel illustrated in FIG. 29H is an example including a light-emitting element 57W for white (W). Here, four light-emitting elements are laterally arranged in a line and the light-receiving element 53 is provided below the four light-emitting elements.

Note that the pixel structure is not limited to the above structure, and a variety of arrangement methods can be employed.

At least part of the structure examples, the drawings corresponding thereto, and the like exemplified in this embodiment can be implemented in combination with the other structure examples, the other drawings, and the like as appropriate.

Embodiment 5

Described in this embodiment is a metal oxide (hereinafter also referred to as an oxide semiconductor) that can be used in an OS transistor described in the above embodiment.

The metal oxide preferably contains at least indium or zinc. In particular, indium and zinc are preferably contained. In addition, aluminum, gallium, yttrium, tin, or the like is preferably contained. Furthermore, one or more kinds selected from boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, cobalt, and the like may be contained.

The metal oxide can be formed by a sputtering method, a chemical vapor deposition (CVD) method such as a metal organic chemical vapor deposition (MOCVD) method, an atomic layer deposition (ALD) method, or the like.

<Classification of Crystal Structure>

Amorphous (including a completely amorphous structure), CAAC (c-axis-aligned crystalline), nc (nanocrystalline), CAC (cloud-aligned composite), single-crystal, and polycrystalline (poly crystal) structures can be given as examples of a crystal structure of an oxide semiconductor.

A crystal structure of a film or a substrate can be analyzed with an X-ray diffraction (XRD) spectrum. For example, evaluation is possible using an XRD spectrum which is obtained by GIXD (Grazing-Incidence XRD) measurement. Note that a GIXD method is also referred to as a thin film method or a Seemann-Bohlin method.

For example, the XRD spectrum of a quartz glass substrate shows a peak with a substantially bilaterally symmetrical shape. On the other hand, the peak of the XRD spectrum of an IGZO film having a crystal structure has a bilaterally asymmetrical shape. The asymmetrical peak of the XRD spectrum clearly shows the existence of crystal in the film or the substrate. In other words, the crystal structure of the film or the substrate cannot be regarded as “amorphous” unless it has a bilaterally symmetrical peak in the XRD spectrum.

A crystal structure of a film or a substrate can also be evaluated with a diffraction pattern obtained by a nanobeam electron diffraction (NBED) method (such a pattern is also referred to as a nanobeam electron diffraction pattern). For example, a halo pattern is observed in the diffraction pattern of the quartz glass substrate, which indicates that the quartz glass substrate is in an amorphous state. Furthermore, not a halo pattern but a spot-like pattern is observed in the diffraction pattern of the IGZO film deposited at room temperature. Thus, it is presumed that the IGZO film deposited at room temperature is in an intermediate state, which is neither a crystal state nor an amorphous state, and it cannot be concluded that the IGZO film is in an amorphous state.

<<Structure of Oxide Semiconductor>>

Oxide semiconductors might be classified in a manner different from the above-described one when classified in terms of the structure. Oxide semiconductors are classified into a single crystal oxide semiconductor and a non-single-crystal oxide semiconductor, for example. Examples of the non-single-crystal oxide semiconductor include the above-described CAAC-OS and nc-OS. Other examples of the non-single-crystal oxide semiconductor include a polycrystalline oxide semiconductor, an amorphous-like oxide semiconductor (a-like OS), and an amorphous oxide semiconductor.

Here, the above-described CAAC-OS, nc-OS, and a-like OS are described in detail.

[CAAC-OS]

The CAAC-OS is an oxide semiconductor that has a plurality of crystal regions each of which has c-axis alignment in a particular direction. Note that the particular direction refers to the film thickness direction of a CAAC-OS film, the normal direction of the surface where the CAAC-OS film is formed, or the normal direction of the surface of the CAAC-OS film. The crystal region refers to a region having a periodic atomic arrangement. When an atomic arrangement is regarded as a lattice arrangement, the crystal region also refers to a region with a uniform lattice arrangement. The CAAC-OS has a region where a plurality of crystal regions are connected in the a-b plane direction, and the region has distortion in some cases. Note that distortion refers to a portion where the direction of a lattice arrangement changes between a region with a uniform lattice arrangement and another region with a uniform lattice arrangement in a region where a plurality of crystal regions are connected. That is, the CAAC-OS is an oxide semiconductor having c-axis alignment and having no clear alignment in the a-b plane direction.

Note that each of the plurality of crystal regions is formed of one or more fine crystals (crystals each of which has a maximum diameter of less than 10 nm). In the case where the crystal region is formed of one fine crystal, the maximum diameter of the crystal region is less than 10 nm. In the case where the crystal region is formed of a large number of fine crystals, the size of the crystal region may be approximately several tens of nanometers.

In the case of an In-M-Zn oxide (the element M is one or more kinds selected from aluminum, gallium, yttrium, tin, titanium, and the like), the CAAC-OS tends to have a layered crystal structure (also referred to as a layered structure) in which a layer containing indium (In) and oxygen (hereinafter, an In layer) and a layer containing the element M, zinc (Zn), and oxygen (hereinafter, an (M,Zn) layer) are stacked. Indium and the element M can be replaced with each other. Therefore, indium may be contained in the (M,Zn) layer. In addition, the element M may be contained in the In layer. Note that Zn may be contained in the In layer. Such a layered structure is observed as a lattice image in a high-resolution transmission electron microscope (TEM) image, for example.

When the CAAC-OS film is subjected to structural analysis by Out-of-plane XRD measurement with an XRD apparatus using θ/2θ scanning, for example, a peak indicating c-axis alignment is detected at 2θ of 31° or around 31°. Note that the position of the peak indicating c-axis alignment (the value of 2θ) may change depending on the kind, composition, or the like of the metal element contained in the CAAC-OS.

For example, a plurality of bright spots are observed in the electron diffraction pattern of the CAAC-OS film. Note that one spot and another spot are observed point-symmetrically with a spot of the incident electron beam passing through a sample (also referred to as a direct spot) as the symmetric center.

When the crystal region is observed from the particular direction, a lattice arrangement in the crystal region is basically a hexagonal lattice arrangement; however, a unit lattice is not always a regular hexagon and is anon-regular hexagon in some cases. Furthermore, a pentagonal or heptagonal lattice arrangement, for example, is included in the distortion in some cases. Note that a clear crystal grain boundary (grain boundary) cannot be observed even in the vicinity of the distortion in the CAAC-OS. That is, formation of a crystal grain boundary is inhibited by the distortion of lattice arrangement. This is probably because the CAAC-OS can tolerate distortion owing to a low density of arrangement of oxygen atoms in the a-b plane direction, an interatomic bond distance changed by substitution of a metal atom, and the like.

A crystal structure in which a clear crystal grain boundary is observed is what is called polycrystal. It is highly probable that the crystal grain boundary becomes a recombination center and captures carriers and thus decreases the on-state current and field-effect mobility of a transistor, for example. Thus, the CAAC-OS in which no clear crystal grain boundary is observed is one of crystalline oxides having a crystal structure suitable for a semiconductor layer of a transistor. Note that Zn is preferably contained to form the CAAC-OS. For example, an In—Zn oxide and an In—Ga—Zn oxide are suitable because they can inhibit generation of a crystal grain boundary as compared with an In oxide.

The CAAC-OS is an oxide semiconductor with high crystallinity in which no clear crystal grain boundary is observed. Thus, in the CAAC-OS, a reduction in electron mobility due to the crystal grain boundary is less likely to occur. Moreover, since the crystallinity of an oxide semiconductor might be decreased by entry of impurities, formation of defects, or the like, the CAAC-OS can be regarded as an oxide semiconductor that has small amounts of impurities and defects (e.g., oxygen vacancies). Thus, an oxide semiconductor including the CAAC-OS is physically stable. Therefore, the oxide semiconductor including the CAAC-OS is resistant to heat and has high reliability. In addition, the CAAC-OS is stable with respect to high temperatures in the manufacturing process (what is called thermal budget). Accordingly, the use of the CAAC-OS for the OS transistor can extend the degree of freedom of the manufacturing process.

[nc-OS]

In the nc-OS, a microscopic region (e.g., a region with a size greater than or equal to 1 nm and less than or equal to 10 nm, in particular, a region with a size greater than or equal to 1 nm and less than or equal to 3 nm) has a periodic atomic arrangement. In other words, the nc-OS includes a fine crystal. Note that the size of the fine crystal is, for example, greater than or equal to 1 nm and less than or equal to 10 nm, particularly greater than or equal to 1 nm and less than or equal to 3 nm; thus, the fine crystal is also referred to as a nanocrystal. Furthermore, there is no regularity of crystal orientation between different nanocrystals in the nc-OS. Thus, the orientation in the whole film is not observed. Accordingly, the nc-OS cannot be distinguished from an a-like OS or an amorphous oxide semiconductor by some analysis methods. For example, when an nc-OS film is subjected to structural analysis by Out-of-plane XRD measurement with an XRD apparatus using θ/2θ scanning, a peak indicating crystallinity is not detected. Furthermore, a diffraction pattern like a halo pattern is observed when the nc-OS film is subjected to electron diffraction (also referred to as selected-area electron diffraction) using an electron beam with a probe diameter larger than the diameter of a nanocrystal (e.g., larger than or equal to 50 nm). Meanwhile, in some cases, a plurality of spots in a ring-like region with a direct spot as the center are observed in the obtained electron diffraction pattern when the nc-OS film is subjected to electron diffraction (also referred to as nanobeam electron diffraction) using an electron beam with a probe diameter nearly equal to or smaller than the diameter of a nanocrystal (e.g., larger than or equal to 1 nm and smaller than or equal to 30 nm).

[A-Like OS]

The a-like OS is an oxide semiconductor having a structure between those of the nc-OS and the amorphous oxide semiconductor. The a-like OS has a void or a low-density region. That is, the a-like OS has lower crystallinity than the nc-OS and the CAAC-OS. Moreover, the a-like OS has higher hydrogen concentration in the film than the nc-OS and the CAAC-OS.

<<Structure of Oxide Semiconductor>>

Next, the above-described CAC-OS is described in detail. Note that the CAC-OS relates to the material composition.

[CAC-OS]

The CAC-OS refers to one composition of a material in which elements constituting a metal oxide are unevenly distributed with a size greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 1 nm and less than or equal to 3 nm, or a similar size, for example. Note that a state in which one or more metal elements are unevenly distributed and regions including the metal element(s) are mixed with a size greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 1 nm and less than or equal to 3 nm, or a similar size in a metal oxide is hereinafter referred to as a mosaic pattern or a patch-like pattern.

In addition, the CAC-OS has a composition in which materials are separated into a first region and a second region to form a mosaic pattern, and the first regions are distributed in the film (this composition is hereinafter also referred to as a cloud-like composition). That is, the CAC-OS is a composite metal oxide having a composition in which the first regions and the second regions are mixed.

Note that the atomic ratios of In, Ga, and Zn to the metal elements contained in the CAC-OS in an In—Ga—Zn oxide are denoted by [In], [Ga], and [Zn], respectively. For example, the first region in the CAC-OS in the In—Ga—Zn oxide has [In] higher than that in the composition of the CAC-OS film. Moreover, the second region has [Ga] higher than that in the composition of the CAC-OS film. For example, the first region has higher [In] and lower [Ga] than the second region. Moreover, the second region has higher [Ga] and lower [In] than the first region.

Specifically, the first region includes indium oxide, indium zinc oxide, or the like as its main component. The second region includes gallium oxide, gallium zinc oxide, or the like as its main component. That is, the first region can be referred to as a region containing In as its main component. The second region can be referred to as a region containing Ga as its main component.

Note that a clear boundary between the first region and the second region cannot be observed in some cases.

In a material composition of a CAC-OS in an In—Ga—Zn oxide that contains In, Ga, Zn, and O, regions containing Ga as a main component are observed in part of the CAC-OS and regions containing In as a main component are observed in part thereof. These regions are randomly dispersed to form a mosaic pattern. Thus, it is suggested that the CAC-OS has a structure in which metal elements are unevenly distributed.

The CAC-OS can be formed by a sputtering method under a condition where a substrate is not heated, for example. Moreover, in the case of forming the CAC-OS by a sputtering method, any one or more selected from an inert gas (typically, argon), an oxygen gas, and a nitrogen gas are used as a deposition gas. The flow rate of the oxygen gas to the total flow rate of the deposition gas in deposition is preferably as low as possible, for example, the flow rate of the oxygen gas to the total flow rate of the deposition gas in deposition is higher than or equal to 0% and lower than 30%, preferably higher than or equal to 0% and lower than or equal to 10%.

For example, energy dispersive X-ray spectroscopy (EDX) is used to obtain EDX mapping, and according to the EDX mapping, the CAC-OS in the In—Ga—Zn oxide has a structure in which the region containing In as its main component (the first region) and the region containing Ga as its main component (the second region) are unevenly distributed and mixed.

Here, the first region has a higher conductivity than the second region. In other words, when carriers flow through the first region, the conductivity of a metal oxide is exhibited. Accordingly, when the first regions are distributed in a metal oxide as a cloud, high field-effect mobility (μ) can be achieved.

The second region has a higher insulating property than the first region. In other words, when the second regions are distributed in a metal oxide, leakage current can be inhibited.

Thus, in the case where a CAC-OS is used for a transistor, by the complementary function of the conducting function due to the first region and the insulating function due to the second region, the CAC-OS can have a switching function (On/Off function). A CAC-OS has a conducting function in part of the material and has an insulating function in another part of the material; as a whole, the CAC-OS has a function of a semiconductor. Separation of the conducting function and the insulating function can maximize each function. Accordingly, when the CAC-OS is used for a transistor, high on-state current (Ion), high field-effect mobility (μ), and excellent switching operation can be achieved.

A transistor using a CAC-OS has high reliability. Thus, the CAC-OS is most suitable for a variety of semiconductor devices such as display devices.

An oxide semiconductor has various structures with different properties. Two or more kinds among the amorphous oxide semiconductor, the polycrystalline oxide semiconductor, the a-like OS, the CAC-OS, the nc-OS, and the CAAC-OS may be included in an oxide semiconductor of one embodiment of the present invention.

<Transistor Including Oxide Semiconductor>

Next, the case where the above oxide semiconductor is used for a transistor is described.

When the above oxide semiconductor is used for a transistor, a transistor with high field-effect mobility can be achieved. In addition, a transistor having high reliability can be achieved.

An oxide semiconductor having a low carrier concentration is preferably used for the transistor. For example, the carrier concentration of an oxide semiconductor is lower than or equal to 1×1017 cm-3, preferably lower than or equal to 1×1015 cm-3, further preferably lower than or equal to 1×1013 cm-3, still further preferably lower than or equal to 1×1011 cm-3, yet further preferably lower than 1×1010 cm-3, and higher than or equal to 1×10−9 cm-3. In order to reduce the carrier concentration of an oxide semiconductor film, the impurity concentration in the oxide semiconductor film is reduced so that the density of defect states can be reduced. In this specification and the like, a state with a low impurity concentration and a low density of defect states is referred to as a highly purified intrinsic or substantially highly purified intrinsic state. Note that an oxide semiconductor having a low carrier concentration may be referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor.

A highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has a low density of defect states and thus has a low density of trap states in some cases.

Electric charge trapped by the trap states in the oxide semiconductor takes a long time to disappear and might behave like fixed electric charge. Thus, a transistor whose channel formation region is formed in an oxide semiconductor with a high density of trap states has unstable electrical characteristics in some cases.

Accordingly, in order to obtain stable electrical characteristics of a transistor, reducing impurity concentration in an oxide semiconductor is effective. In order to reduce the impurity concentration in the oxide semiconductor, it is preferable that the impurity concentration in an adjacent film be also reduced. Examples of impurities include hydrogen, nitrogen, an alkali metal, an alkaline earth metal, iron, nickel, and silicon.

<Impurity>

Here, the influence of each impurity in the oxide semiconductor is described.

When silicon or carbon, which is one of Group 14 elements, is contained in the oxide semiconductor, defect states are formed in the oxide semiconductor. Thus, the concentration of silicon or carbon in the oxide semiconductor and the concentration of silicon or carbon in the vicinity of an interface with the oxide semiconductor (the concentration obtained by secondary ion mass spectrometry (SIMS)) are each set lower than or equal to 2×1018 atoms/cm3, preferably lower than or equal to 2×1017 atoms/cm3.

When the oxide semiconductor contains an alkali metal or an alkaline earth metal, defect states are formed and carriers are generated in some cases. Accordingly, a transistor including an oxide semiconductor that contains an alkali metal or an alkaline earth metal tends to have normally-on characteristics. Thus, the concentration of an alkali metal or an alkaline earth metal in the oxide semiconductor, which is obtained by SIMS, is set lower than or equal to 1×1018 atoms/cm3, preferably lower than or equal to 2×1016 atoms/cm3.

An oxide semiconductor containing nitrogen easily becomes n-type by generation of electrons serving as carriers and an increase in carrier concentration. Thus, a transistor using an oxide semiconductor containing nitrogen as the semiconductor tends to have normally-on characteristics. When nitrogen is contained in the oxide semiconductor, a trap state is sometimes formed. This might make the electrical characteristics of the transistor unstable. Therefore, the concentration of nitrogen in the oxide semiconductor, which is obtained by SIMS, is set lower than 5×1019 atoms/cm3, preferably lower than or equal to 5×1018 atoms/cm3, further preferably lower than or equal to 1×1018 atoms/cm3, still further preferably lower than or equal to 5×1017 atoms/cm3.

Hydrogen contained in the oxide semiconductor reacts with oxygen bonded to a metal atom to be water, and thus forms an oxygen vacancy in some cases. Entry of hydrogen into the oxygen vacancy generates an electron serving as a carrier in some cases. Furthermore, bonding of part of hydrogen to oxygen bonded to a metal atom causes generation of an electron serving as a carrier in some cases. Thus, a transistor using an oxide semiconductor containing hydrogen is likely to have normally-on characteristics. Accordingly, hydrogen in the oxide semiconductor is preferably reduced as much as possible. Specifically, the hydrogen concentration in the oxide semiconductor, which is obtained by SIMS, is set lower than 1×1020 atoms/cm3, preferably lower than 1×1019 atoms/cm3, further preferably lower than 5×1018 atoms/cm3, still further preferably lower than 1×1018 atoms/cm3.

When an oxide semiconductor with sufficiently reduced impurities is used for the channel formation region of the transistor, stable electrical characteristics can be given.

At least part of the structure examples, the drawings corresponding thereto, and the like exemplified in this embodiment can be implemented in combination with the other structure examples, the other drawings, and the like as appropriate.

Embodiment 6

In this embodiment, electronic devices of embodiments of the present invention will be described with reference to FIG. 30 to FIG. 32 .

An electronic device in this embodiment includes the display device of one embodiment of the present invention. For example, the display device of one embodiment of the present invention can be used in a display portion of the electronic device. The display device of one embodiment of the present invention has a function of sensing light, and thus can perform biological authentication with the display portion or detect a touch operation (a contact or an approach). Consequently, the electronic device can have improved functionality and convenience, for example.

Examples of electronic devices include a digital camera, a digital video camera, a digital photo frame, a mobile phone, a portable game console, a portable information terminal, and an audio reproducing device, in addition to electronic devices with a relatively large screen, such as a television device, a desktop or laptop personal computer, a monitor of a computer or the like, digital signage, and a large game machine such as a pachinko machine.

The electronic device in this embodiment may include a sensor (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, a chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, a smell, or infrared rays).

The electronic device in this embodiment can have a variety of functions. For example, the electronic device can have a function of displaying a variety of information (a still image, a moving image, a text image, and the like) on the display portion, a touch panel function, a function of displaying a calendar, date, time, and the like, a function of executing a variety of software (programs), a wireless communication function, and a function of reading out a program or data stored in a recording medium.

An electronic device 6500 illustrated in FIG. 30A is a portable information terminal that can be used as a smartphone.

The electronic device 6500 includes a housing 6501, a display portion 6502, a power button 6503, buttons 6504, a speaker 6505, a microphone 6506, a camera 6507, a light source 6508, and the like. The display portion 6502 has a touch panel function.

The display device of one embodiment of the present invention can be used in the display portion 6502.

FIG. 30B is a schematic cross-sectional view including an end portion of the housing 6501 on the microphone 6506 side.

A protection member 6510 having a light-transmitting property is provided on the display surface side of the housing 6501, and a display device 6511, an optical member 6512, a touch sensor panel 6513, a printed circuit board 6517, a battery 6518, and the like are provided in a space surrounded by the housing 6501 and the protection member 6510.

The display device 6511, the optical member 6512, and the touch sensor panel 6513 are fixed to the protection member 6510 with an adhesive layer (not illustrated).

Part of the display device 6511 is folded back in a region outside the display portion 6502, and an FPC 6515 is connected to the part that is folded back. An IC 6516 is mounted on the FPC 6515. The FPC 6515 is connected to a terminal provided on the printed circuit board 6517.

A flexible display of one embodiment of the present invention can be used as the display device 6511. Thus, an extremely lightweight electronic device can be achieved. Since the display device 6511 is extremely thin, the battery 6518 with high capacity can be mounted with the thickness of the electronic device controlled. An electronic device with a narrow frame can be achieved when part of the display device 6511 is folded back so that the portion connected to the FPC 6515 is provided on the rear side of a pixel portion.

Using the display device of one embodiment of the present invention as the display device 6511 allows image capturing on the display portion 6502. For example, an image of a fingerprint is captured by the display device 6511; thus, fingerprint identification can be performed.

By further including the touch sensor panel 6513, the display portion 6502 can have a touch panel function. A variety of types such as a capacitive type, a resistive type, a surface acoustic wave type, an infrared type, an optical type, and a pressure-sensitive type can be used for the touch sensor panel 6513. Alternatively, the display device 6511 may function as a touch sensor; in such a case, the touch sensor panel 6513 is not necessarily provided.

FIG. 30A illustrates an example of a television device. In a television device 7100, a display portion 7000 is incorporated in a housing 7101. Here, a structure in which the housing 7101 is supported by a stand 7103 is illustrated.

The display device of one embodiment of the present invention can be used in the display portion 7000.

Operation of the television device 7100 illustrated in FIG. 31A can be performed with an operation switch provided in the housing 7101 or a separate remote controller 7111. Alternatively, the display portion 7000 may include a touch sensor, and the television device 7100 may be operated by a touch on the display portion 7000 with a finger or the like. The remote controller 7111 may include a display portion for displaying information output from the remote controller 7111. With operation keys or a touch panel provided in the remote controller 7111, channels and volume can be controlled, and videos displayed on the display portion 7000 can be controlled.

Note that the television device 7100 has a structure in which a receiver, a modem, and the like are provided. A general television broadcast can be received with the receiver. When the television device is connected to a communication network with or without wires via the modem, one-way (from a transmitter to a receiver) or two-way (between a transmitter and a receiver or between receivers, for example) data communication can be performed.

FIG. 31B illustrates an example of a laptop personal computer. A laptop personal computer 7200 includes a housing 7211, a keyboard 7212, a pointing device 7213, an external connection port 7214, and the like. The display portion 7000 is incorporated in the housing 7211.

The display device of one embodiment of the present invention can be used in the display portion 7000.

FIG. 31C and FIG. 31D illustrate examples of digital signage.

Digital signage 7300 illustrated in FIG. 31C includes a housing 7301, the display portion 7000, a speaker 7303, and the like. Furthermore, the digital signage can include an LED lamp, operation keys (including a power switch or an operation switch), a connection terminal, a variety of sensors, a microphone, and the like.

FIG. 31D shows digital signage 7400 attached to a cylindrical pillar 7401. The digital signage 7400 includes the display portion 7000 provided along a curved surface of the pillar 7401.

The display device of one embodiment of the present invention can be used in the display portion 7000 in FIG. 31C and FIG. 31D.

A larger area of the display portion 7000 can increase the amount of information that can be provided at a time. The larger display portion 7000 attracts more attention, so that the advertising effectiveness can be enhanced, for example.

The use of a touch panel in the display portion 7000 is preferable because in addition to display of a still image or a moving image on the display portion 7000, intuitive operation by a user is possible. Moreover, for an application for providing information such as route information or traffic information, usability can be enhanced by intuitive operation.

As illustrated in FIG. 31C and FIG. 31D, it is preferable that the digital signage 7300 or the digital signage 7400 can work with an information terminal 7311 or an information terminal 7411, such as a smartphone a user has, through wireless communication. For example, information of an advertisement displayed on the display portion 7000 can be displayed on a screen of the information terminal 7311 or the information terminal 7411. By operation of the information terminal 7311 or the information terminal 7411, display on the display portion 7000 can be switched.

It is possible to make the digital signage 7300 or the digital signage 7400 execute a game with use of the screen of the information terminal 7311 or the information terminal 7411 as an operation means (controller). Thus, an unspecified number of users can join in and enjoy the game concurrently.

Electronic devices illustrated in FIG. 32A to FIG. 32F include a housing 9000, a display portion 9001, a speaker 9003, an operation key 9005 (including a power switch or an operation switch), a connection terminal 9006, a sensor 9007 (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, a chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, a smell, or infrared rays), a microphone 9008, and the like.

The electronic devices illustrated in FIG. 32A to FIG. 32F have a variety of functions. For example, the electronic devices can have a function of displaying a variety of information (a still image, a moving image, a text image, and the like) on the display portion, a touch panel function, a function of displaying a calendar, date, time, and the like, a function of controlling processing with the use of a variety of software (programs), a wireless communication function, and a function of reading out and processing a program or data stored in a recording medium. Note that the functions of the electronic devices are not limited thereto, and the electronic devices can have a variety of functions. The electronic devices may include a plurality of display portions. The electronic devices may each include a camera or the like and have a function of taking a still image or a moving image and storing the taken image in a recording medium (an external recording medium or a recording medium incorporated in the camera), a function of displaying the taken image on the display portion, or the like.

The details of the electronic devices illustrated in FIG. 32A to FIG. 32F are described below.

FIG. 32A is a perspective view illustrating a portable information terminal 9101. The portable information terminal 9101 can be used as a smartphone, for example. Note that the portable information terminal 9101 may be provided with the speaker 9003, the connection terminal 9006, the sensor 9007, or the like. The portable information terminal 9101 can display letters and image information on its plurality of surfaces. FIG. 32A illustrates an example where three icons 9050 are displayed. Information 9051 indicated by dashed rectangles can be displayed on another surface of the display portion 9001. Examples of the information 9051 include notification of reception of an e-mail, SNS, an incoming call, or the like, the title and sender of an e-mail, SNS, or the like, the date, the time, remaining battery, and the reception strength of an antenna. Alternatively, the icon 9050 or the like may be displayed at the position where the information 9051 is displayed.

FIG. 32B is a perspective view illustrating a portable information terminal 9102. The portable information terminal 9102 has a function of displaying information on three or more surfaces of the display portion 9001. Here, an example in which information 9052, information 9053, and information 9054 are displayed on different surfaces is illustrated. For example, a user can check the information 9053 displayed at a position that can be observed from above the portable information terminal 9102, with the portable information terminal 9102 put in a breast pocket of his/her clothes. The user can seethe display without taking out the portable information terminal 9102 from the pocket and decide whether to answer the call, for example.

FIG. 32C is a perspective view illustrating a watch-type portable information terminal 9200. The display portion 9001 is provided such that its display surface is curved, and display can be performed along the curved display surface. Mutual communication between the portable information terminal 9200 and, for example, a headset capable of wireless communication enables hands-free calling. With the connection terminal 9006, the portable information terminal 9200 can perform mutual data transmission with another information terminal and charging. Note that the charging operation may be performed by wireless power feeding.

FIG. 32D to FIG. 32F are perspective views illustrating a foldable portable information terminal 9201. FIG. 32D is a perspective view of an opened state of the portable information terminal 9201, FIG. 32F is a perspective view of a folded state thereof, and FIG. 32E is a perspective view of a state in the middle of change from one of FIG. 32D and FIG. 32F to the other. The portable information terminal 9201 is highly portable in the folded state and is highly browsable in the opened state because of a seamless large display region. The display portion 9001 of the portable information terminal 9201 is supported by three housings 9000 joined by hinges 9055. For example, the display portion 9001 can be curved with a radius of curvature greater than or equal to 0.1 mm and less than or equal to 150 mm.

At least part of this embodiment can be implemented in combination with the other embodiments described in this specification as appropriate.

REFERENCE NUMERALS

A0: input terminal, A1: input terminal, A2: input terminal, AD0: selection signal, AD1: selection signal, AD2: selection signal, C1: capacitor, C2: capacitor, C3: capacitor, CS1: capacitor, CS2: capacitor, GL1: wiring, GL2: wiring, In1: input terminal, In2: input terminal, In3: input terminal, In4: input terminal, In5: input terminal, In6: input terminal, In7: input terminal, In8: input terminal, L1: inverter circuit, L2: inverter circuit, L3: inverter circuit, L4: inverter circuit, LP1: low-pass filter, LP2: low-pass filter, LP3: low-pass filter, M1: transistor, M2: transistor, M3: transistor, M4: transistor, M5: transistor, M6: transistor, M7: transistor, M8: transistor, M10: transistor, M11: transistor, M12: transistor, M13: transistor, M14: transistor, N1: node, N2: node, N3: node, N4: node, N5: node, N6: node, N7: node, N8: node, Ot1: output terminal, Ot2: output terminal, R1: resistor, R2: resistor, R3: resistor, R4: resistor, R5: resistor, R6: resistor, R7: resistor, R8: resistor, R9: resistor, R10: resistor, R11: resistor, R13: resistor, S1: transistor, S2: transistor, S3: transistor, S4: transistor, S5: transistor, S6: transistor, S7: transistor, S8: transistor, S9: transistor, S10: transistor, S11: transistor, S12: transistor, S13: transistor, S14: transistor, S15: transistor, S16: transistor, SL1: wiring, SL2: wiring, SL3: wiring, SW1: switch, SW2: switch, SW3: switch, V0: reset potential, V0L: wiring, V1: grayscale signal, V2: grayscale signal, V3: grayscale signal, V5: grayscale signal, V6: grayscale signal, V7: grayscale signal, V8: grayscale signal, VL1: wiring, VL2: wiring, VL3: wiring, 10: display device, 11: display portion, 12: driver circuit, 12A: driver circuit, 12B: circuit, 12G: circuit, 12R: circuit, 13: driver circuit, 14: driver circuit, 15: circuit, 15A: circuit, 20 aB: subpixel, 20 aG: subpixel, 20 aR: subpixel, 20B: subpixel, 20G: subpixel, 20R: subpixel, 21: pixel, 21B: subpixel, 21G: subpixel, 21R: subpixel, 22: circuit, 22 aB: circuit, 22 aG: circuit, 22 aR: circuit, 22B: circuit, 22G: circuit, 22P: imaging pixel, 22R: circuit, 30: pixel, 30 a: pixel, 30B: pixel, 30G: pixel, 50: display device, 51: substrate, 52: substrate, 53: light-receiving element, 55: functional layer, 57: light-emitting element, 57B: light-emitting element, 57G: light-emitting element, 57R: light-emitting element, 57W: light-emitting element, 60: finger, 61: contact portion, 62: fingerprint, 63: image-capturing range, 65: stylus, 66: path, 71: latch circuit, 72: level shifter circuit, 73: semiconductor device, 74: buffer circuit, 81: circuit, 82: lamp signal generation circuit, 83: comparison circuit, 84: counter circuit, 100: digital-analog converter circuit, 100A: display device, 100B: display device, 100C: display device, 110: level shifter circuit, 110_n: level shifter circuit, 110_1: level shifter circuit, 112: common layer, 114: common layer, 115: common electrode, 120: semiconductor device, 120 a: wiring, 120 b: wiring, 121: pass transistor circuit, 121 a: circuit, 121A: pass transistor circuit, 121 b: circuit, 121 c: circuit, 122: voltage generation circuit, 122 a: output terminal, 122 b: output terminal, 122 c: output terminal, 122 d: output terminal, 122 e: output terminal, 122 f output terminal, 122 g: output terminal, 122 h: output terminal, 123: low-pass filter, 123 a: input terminal, 123A: low-pass filter, 123 b: input terminal, 123 c: output terminal, 130: buffer circuit, 130 a: amplifier circuit, 130 b: output resistor, 140: latch circuit, 142: adhesive layer, 143: space, 151: substrate, 152: substrate, 153: substrate, 154: substrate, 155: adhesive layer, 162: display portion, 164: circuit, 165: wiring, 166: conductive layer, 172: FPC, 173: IC, 180: electrode, 181: hole-injection layer, 182: hole-transport layer, 182B: hole-transport layer, 182G: hole-transport layer, 182R: hole-transport layer, 183: active layer, 184: electron-transport layer, 185: electron-injection layer, 186: layer, 189: electrode, 190B: light-emitting element, 190G: light-emitting element, 190MER: light-emitting and light-receiving element, 191: pixel electrode, 192: buffer layer, 192B: buffer layer, 192G: buffer layer, 192R: buffer layer, 193: light-emitting layer, 193B: light-emitting layer, 193G: light-emitting layer, 193R: light-emitting layer, 194: buffer layer, 194B: buffer layer, 194G: buffer layer, 194R: buffer layer, 195: protective layer, 201: transistor, 202: transistor, 204: connection portion, 205: transistor, 206: transistor, 207: transistor, 208: transistor, 209: transistor, 210: transistor, 211: insulating layer, 212: insulating layer, 213: insulating layer, 214: insulating layer, 215: insulating layer, 216: partition, 218: insulating layer, 221: conductive layer, 222 a: conductive layer, 222 b: conductive layer, 223: conductive layer, 225: insulating layer, 228: region, 231: semiconductor layer, 231 i: channel formation region, 231 n: low-resistance region, 242: connection layer, 310A: display device, 310B: display device, 310C: display device, 321B: light, 321G: light, 321R: light, 322: light, 323: light, 324: reflected light, 342: transistor, 347B: light-emitting element, 347G: light-emitting element, 347MER: light-emitting and light-receiving element, 350A: display device, 350B: display device, 351: substrate, 352: finger, 353: layer, 355: layer, 357: layer, 359: substrate, 6500: electronic device, 6501: housing, 6502: display portion, 6503: power source button, 6504: button, 6505: speaker, 6506: microphone, 6507: camera, 6508: light source, 6510: protection member, 6511: display device, 6512: optical member, 6513: touch sensor panel, 6515: FPC, 6516: IC, 6517: printed circuit board, 6518: battery, 7000: display portion, 7100: television device, 7101: housing, 7103: stand, 7111: remote controller, 7200: laptop personal computer, 7211: housing, 7212: keyboard, 7213: pointing device, 7214: external connection port, 7300: digital signage, 7301: housing, 7303: speaker, 7311: information terminal, 7400: digital signage, 7401: pillar, 7411: information terminal, 9000: housing, 9001: display portion, 9003: speaker, 9005: operation key, 9006: connection terminal, 9007: sensor, 9008: microphone, 9050: icon, 9051: information, 9052: information, 9053: information, 9054: information, 9055: hinge, 9101: portable information terminal, 9102: portable information terminal, 9200: portable information terminal, 9201: portable information terminal 

The invention claimed is:
 1. A semiconductor device comprising: a first circuit; a second circuit; a third circuit; a plurality of input terminals; a first output terminal; and a second output terminal, wherein the first circuit comprises a plurality of first transistors functioning as pass transistors, wherein the second circuit comprises a plurality of second transistors functioning as pass transistors, wherein a number of the first transistors is larger than a number of the second transistors, wherein the first circuit is cascaded to the second circuit, wherein a gate of the first transistor included in the first circuit is supplied with a first signal, wherein a gate of the second transistor included in the second circuit is supplied with a second signal, wherein the third circuit comprises a fourth n-channel transistor and a fourth p-channel transistor, wherein one of a source and a drain of the fourth n-channel transistor is electrically connected to the first output terminal through a first node, wherein one of a source and a drain of the fourth p-channel transistor is electrically connected to the second output terminal through a second node, wherein the first circuit is supplied with first grayscale signals having different potentials through x of the input terminals and x is a positive integer, wherein the first circuit selects y of the first grayscale signals with the first signal and y is a positive integer and y<x, wherein the second circuit is supplied with they first grayscale signals, wherein the second circuit outputs z of they first grayscale signals to one of the first output terminal and the second output terminal with the second signal and z is a positive integer and z<y, wherein the other of the source and the drain of the fourth n-channel transistor and the other of the source and the drain of the fourth p-channel transistor are supplied with any one of the first grayscale signals as a second grayscale signal, and wherein one of the first node and the second node is supplied with the second grayscale signal as a precharge potential.
 2. The semiconductor device according to claim 1, wherein the first circuit comprises a first n-channel transistor, a second n-channel transistor, a first p-channel transistor, and a second p-channel transistor, wherein the second circuit comprises a third n-channel transistor and a third p-channel transistor, wherein the first signal is supplied to the first n-channel transistor and the first p-channel transistor, wherein an inverted signal of the first signal is supplied to the second n-channel transistor and the second p-channel transistor, wherein the second signal is supplied to the third p-channel transistor, and wherein an inverted signal of the second signal is supplied to the third n-channel transistor.
 3. The semiconductor device according to claim 2, wherein one of a source and a drain of each of the first n-channel transistor, the second n-channel transistor, the first p-channel transistor, and the second p-channel transistor that are included in the first circuit is supplied with one of the first grayscale signals through a corresponding one of the input terminals, and wherein the other of a source and a drain of each of the third n-channel transistor and the third p-channel transistor outputs any one of the first grayscale signals to a corresponding one of the first output terminal and the second output terminal.
 4. The semiconductor device according to claim 3, wherein the other of the source and the drain of each of the third n-channel transistor and the third p-channel transistor that are included in the second circuit is electrically connected to a low-pass filter.
 5. The semiconductor device according to claim 4, wherein the low-pass filter comprises a first resistor, a second resistor, and a capacitor, wherein the other of the source and the drain of the third p-channel transistor is electrically connected to one electrode of the first resistor, wherein the other of the source and the drain of the third n-channel transistor is electrically connected to one electrode of the second resistor, and wherein the other electrode of the first resistor and the other electrode of the second resistor are electrically connected to one electrode of the capacitor and an output terminal of the low-pass filter.
 6. The semiconductor device according to claim 5, wherein a gate of the fourth n-channel transistor is supplied with a third signal, and a gate of the fourth p-channel transistor is supplied with an inverted signal of the third signal.
 7. A semiconductor device comprising: a latch circuit; a boosting circuit; a selection circuit; and a buffer circuit, wherein the selection circuit comprises a pass transistor circuit, a voltage generation circuit outputting a plurality of potentials, and a low-pass filter, wherein the pass transistor circuit comprises a plurality of first transistors, a plurality of second transistors, a third transistor, and a fourth transistor functioning as pass transistors, a plurality of input terminals, a first output terminal, a second output terminal, wherein a number of the first transistors is larger than a number of the second transistors, wherein the first transistor is cascaded to the second transistor, wherein one of a source and a drain of the third transistor is electrically connected to the first output terminal through a first node, wherein one of a source and a drain of the fourth transistor is electrically connected to the second output terminal through a second node, wherein the other of the source and the drain of the third transistor and the other of the source and the drain of the fourth transistor is supplied with one of the potentials output from the voltage generation circuit, wherein one of the first node and the second node is supplied with the one of the potentials as a precharge potential, wherein a data signal supplied to the latch circuit is supplied to the boosting circuit, wherein the boosting circuit generates a selection signal by boosting a potential of the data signal, wherein with the selection signal, the plurality of the first transistors and the plurality of the second transistors that are included in the pass transistor circuit are brought into an on state or an off state so that any one of the potentials generated by the voltage generation circuit is selected and output to the low-pass filter, wherein the buffer circuit is supplied with the potential from which noise is removed by the low-pass filter, and wherein the buffer circuit outputs the potential. 